20 Conduit Street, London, W1S 2XW

20 Conduit Street, London, W1S 2XW — City of Westminster Council — Appeal Decisions Site visit made on 11 November 2025 by Juliet Rogers BA (Hons) MA MRTPI an Inspector appointed by the Secretary of State Decision date: 8 December 2025 Appeal A Ref: APP/X5990/W/25/3369382 20 Conduit Street, London W1S 2XW • The appeal is made under section 78 of the Town and Country Planning Act 1990 (as amended) against a refusal to grant planning permission. • The appeal is made by Oilinvest (Netherlands) B.V. against the decision of City of Westminster Council. • The application Ref is 25/02291/FULL. The development proposed is an extension to the rear wing at fifth floor level; replacement of mansard roof slope to rear wing at fourth floor level; replacement windows within existing openings; cleaning and repairs of listed façade; lift shaft extension; replacement of redundant AOV and new plant to roof level. Appeal B Ref: APP/X5990/Y/25/3369381 20 Conduit Street, London W1S 2XW • The appeal is made under section 20 of the Planning (Listed Buildings and Conservation Areas) Act 1990 (as amended) against a refusal to grant listed building consent. • The appeal is made by Oilinvest (Netherlands) B.V. against the decision of City of Westminster Council. • The application Ref is 25/02292/LBC.

20 Conduit Street, London, W1S 2XW — City of Westminster Council — Appeal Decisions • The works proposed are as per Appeal A. Decisions 1. Appeal A is dismissed. 2. Appeal B is dismissed. Preliminary Matters 3. As the site comprises part of a listed building, I have had regard to sections 16(2) and 66(1) of the Planning (Listed Buildings and Conservation Areas) Act 1990 (as amended) (the Act). I have also had regard to section 72(1) of the Act as the site is located within a conservation area. 4. Although the Council is in the process of undertaking a partial review of the City of Westminster City Plan 2019-2040 (City Plan), no policies therein have been presented as relevant to this appeal. I have, therefore, determined this case in accordance with the extant City Plan. Main Issue 5. The main issue of both appeals is whether the proposal would preserve the Grade II listed building of 20, Conduit Street W11, or its setting, or any of the features of special architectural or historic interest that it possesses; the extent to which the 1 List Entry Number: 1066974, date first listed 1 December 1987 https://www.gov.uk/planning-inspectorate

20 Conduit Street, London, W1S 2XW — City of Westminster Council — Appeal Decisions Appeal Decisions APP/X5990/W/25/3369382, APP/X5990/Y/25/3369381 proposal would preserve or enhance the character or appearance of the Mayfair Conservation Area (MCA); and whether the proposal would preserve the setting of the nearby Grade I listed Church of St George, Vestry and Obelisks2 (the Church). Reasons 6. The appeal scheme relates to the existing office space on floors one to four inclusive of the listed building, together with the plant room and lift overrun on the fifth floor. The remainder of the building, comprising a shop on the ground floor and basement levels, lies outside the appeal site. 7. Designed by notable architects Treadwell and Martin and built around 1900, the façade of the listed building is a key part of its special architectural interest, with a seven-lights wide, mullioned oriel bay window centrepiece extending across first, second and third floor levels. Classically arranged openings in this prominent centrepiece, together with ornate scrolls, carved stone side pilaster strips and curved Dutch gable with moulded coping to the front elevation, make a positive contribution to the special interest of the listed building. 8.

20 Conduit Street, London, W1S 2XW — City of Westminster Council — Appeal Decisions Although in place when the property was listed, the bulk, scale and materials of the rear wing indicates it is likely to have been constructed at a later date than the front part of the building. Nonetheless, it forms part of the listing building, despite the lack of reference to or specific exclusion of it within the official listing. Other additions and alterations have been made to the appeal property, including the mansard roof profile at fourth floor level and the installation of dark grey metal casement windows throughout. Due to their scale, bulk and materials, these features detract from the special architectural or historical interest of the listed building. 9. Therefore, insofar as is relevant to the appeal scheme, the special interest of the listed building is derived from the detail and condition of the features of the architect-designed façade, including the arrangement and proportions of the window openings above ground floor. The longstanding commercial use of the building also forms part of the building’s special historical interest. 10. The proposals comprise the removal of the unsympathetic mansard roof profile together with the provision of additional office space at fifth floor level.

20 Conduit Street, London, W1S 2XW — City of Westminster Council — Appeal Decisions The relocation of the existing plant is also proposed to facilitate the increase in office floorspace and the lift shaft overrun extended to a similar height as the building’s existing ridgeline. Although the new fifth floor accommodation would not project to the full depth of the rear wing, nevertheless its substantial bulk and boxed form would dominate the roofscape of the listed building. The use of metal cladding and single paned windows would accentuate this aesthetic through the introduction of an incongruous material on the heritage asset. It would not, therefore, be a subservient addition to the front section of the building. 11. Although the relocated plant area would be sited back from the front elevation, thereby being partially screened by the Dutch gable, it would be taller than the building’s existing chimney and extend beyond the roofscape. Furthermore, the extended lift overrun would be a similar height to the existing ridgeline of the listed building.

20 Conduit Street, London, W1S 2XW — City of Westminster Council — Appeal Decisions While views of these additions, as well as the new metal guarding, may not be readily available from street level, the roofscape would still be visible from 2 List Entry Number: 1235638, date first listed 24 February 1958 https://www.gov.uk/planning-inspectorate 2

20 Conduit Street, London, W1S 2XW — City of Westminster Council — Appeal Decisions While views of these additions, as well as the new metal guarding, may not be readily available from street level, the roofscape would still be visible from 2 List Entry Number: 1235638, date first listed 24 February 1958 https://www.gov.uk/planning-inspectorate 2

20 Conduit Street, London, W1S 2XW — City of Westminster Council — Appeal Decisions Appeal Decisions APP/X5990/W/25/3369382, APP/X5990/Y/25/3369381 within and atop buildings of a similar or greater height in the surrounding area, including in conjunction with the listed building’s façade. The result would be the introduction of further visual clutter onto the roofscape which detracts from the front elevation. In any event, listed buildings are safeguarded for their inherent architectural and historic interest, irrespective of the availability of public views of it. Therefore, the fact that much of the proposal would not be visible from public locations within the wider area does not make harmful development or works acceptable. 12. The expansion of office space in a Central Activities Zone (CAZ) is, in principle, supported. As is the removal and/or replacement of features the detract from the special architectural interest of the listed building, including the metal casement windows and the mansard roof. The proposed cleaning of the building’s façade would also be an enhancement to the listed building. 13. However, in the case of the windows, the proposed plans indicate the use of composite frames, thereby replacing one unsympathetic material with another.

20 Conduit Street, London, W1S 2XW — City of Westminster Council — Appeal Decisions While the appellant refers to the style of the windows as per those found historically on the building, no other details are provided to verify this assertion. Therefore, I cannot conclude with certainty that there would be no loss of historic fabric resulting from the installation of replacement windows or that the special architectural or historic interest of the listed building would be preserved. 14. The MCA covers an area predominantly comprising tall, terraced buildings many with classically influenced vernacular, in formal, well-defined blocks formed by a gridded pattern of streets. Some routes, including Conduit Street, cut across these blocks at an angle, thereby creating straight vistas punctuated by built form at the end of these routes. The mixed commercial use of the area, at street level and vertically within the buildings, is also an important feature of the MCA, particularly given its proximity to Saville Row and Regent Street. These characteristics, along with the abundance of well-maintained building façades are key elements from which the significance of the MCA is derived. 15.

20 Conduit Street, London, W1S 2XW — City of Westminster Council — Appeal Decisions A variety of plot widths, façade features, types of materials and colours are discernible across the terrace within which the listed building is located. Nonetheless, the formal relationship of the built form to the street, similar building heights and classically proportioned fenestration arrangements of the façades represent good examples of the elements of the MCA’s significance, together with the mix of uses, both at street level and vertically within the buildings. As these are characteristics and features of the appeal property, it therefore makes a positive contribution to the significance of the MCA. 16. Given the importance of the building façades within the MCA, the lack of clarity around the design of the replacement windows and the impact of any installation works on the historic fabric of the listed building undermines the positive effect which would be derived from the removal of the existing unsympathetic casements. Furthermore, the introduction of the additional bulk and height to the listed building above the rear wing, alongside the visual clutter to the roofscape resulting from the extended lift overrun and relocated plant, would be harmful to the appearance of the MCA. 17.

20 Conduit Street, London, W1S 2XW — City of Westminster Council — Appeal Decisions The Grade I listed Church is located to the rear of the appeal site, on the corner of St George Street and Maddox Street. Its Corinthian columned portico with side https://www.gov.uk/planning-inspectorate 3

20 Conduit Street, London, W1S 2XW — City of Westminster Council — Appeal Decisions The Grade I listed Church is located to the rear of the appeal site, on the corner of St George Street and Maddox Street. Its Corinthian columned portico with side https://www.gov.uk/planning-inspectorate 3

20 Conduit Street, London, W1S 2XW — City of Westminster Council — Appeal Decisions Appeal Decisions APP/X5990/W/25/3369382, APP/X5990/Y/25/3369381 obelisks is an impressive structure within the street scene, not only due to its scale but also its siting forward of the prevailing building line in the block and the contrasting vernacular in the surroundings. A clock tower sits above the portico and includes a belfry and cupola considered to be Wren inspired features. These attributes, together with the quality and condition of the Church’s Portland ashlar construction, contribute to the special historical and architectural interest of the listed building. 18. The frontage and tower are important elements that signify the presence of the ecclesiastical building and would, at the time of its construction between 1720-24, been significant landmarks in the area. Given the now substantially built-up urban area immediately surrounding the Church, sight of the façade and tower from public spaces is primarily constrained to the vistas along St George Street and Maddox Street when travelling from Grosvenor Street.

20 Conduit Street, London, W1S 2XW — City of Westminster Council — Appeal Decisions Nonetheless, the formality of the gridded blocks, the relationship between the built form and the street and the abundance of vernacular architectural features nearby make a positive contribution to the setting of the Grade I listed Church. 19. Part of the southern side elevation of the Church is visible from the rear of the appeal site, beyond and over the closet wings and rear extensions to other properties in the block. However, an appreciation of this side elevation is largely lost within the variety of heights, ages and bulks of the rear structures amalgamated within this part of the Church’s setting. As the tallest feature of the church, the tower is a more obvious and recognisable feature in the views from the appeal site, with those from the fourth floor and roof more pronounced. Despite the height of the tower, as other taller buildings have been constructed in the wider area, its panoramic landmark function has been diminished. Furthermore, the appeal site, including the rear wing, is not experienced in the same views or vistas as the Church’s façade or tower. I conclude, therefore, that the proposal would preserve the setting of the Grade I listed Church of St George. 20.

20 Conduit Street, London, W1S 2XW — City of Westminster Council — Appeal Decisions Nevertheless, I have found that the proposal would not preserve the Grade II listed building of 20, Conduit Street W1, or its setting, or the features of special or historic interest it possesses. Nor would it preserve the character or appearance of the MCA. Therefore, it would conflict with policies 38, 39 and 40 of the City Plan insofar as they require development to contribute positively to Westminster’s townscape and streetscape. 21. The proposal also fails to satisfy the requirements of the Act. The level of harm in this case would be less than substantial. Taking into account the proposed bulk, scale and use of materials would create an insubordinate and incongruous rear wing, the magnitude of this harm would be towards the higher end of the less than substantial scale. In respect to the MCA, the level of harm would be moderate due to my conclusions relating to the lack of details of the replacement windows and the bulk and aesthetics of the additional office space.

20 Conduit Street, London, W1S 2XW — City of Westminster Council — Appeal Decisions In these circumstances the Framework states that harm to or loss of the significance of a designated heritage asset requires clear and convincing justification and should be weighed against the public benefits which would be derived from it, including securing its optimum viable use, where appropriate. 22. The proposal would lead to economic benefits from an increase in the amount of commercial floorspace within a CAZ and the overall improvement in the facilities within the existing office accommodation. The principle of additional commercial https://www.gov.uk/planning-inspectorate 4

20 Conduit Street, London, W1S 2XW — City of Westminster Council — Appeal Decisions In these circumstances the Framework states that harm to or loss of the significance of a designated heritage asset requires clear and convincing justification and should be weighed against the public benefits which would be derived from it, including securing its optimum viable use, where appropriate. 22. The proposal would lead to economic benefits from an increase in the amount of commercial floorspace within a CAZ and the overall improvement in the facilities within the existing office accommodation. The principle of additional commercial https://www.gov.uk/planning-inspectorate 4

20 Conduit Street, London, W1S 2XW — City of Westminster Council — Appeal Decisions Appeal Decisions APP/X5990/W/25/3369382, APP/X5990/Y/25/3369381 floorspace within this area is therefore acceptable and supported by Policy 13 of the City Plan, particularly given the need for new space to meet existing and future demand. The Framework also places significant weight to the need to support economic growth and productivity. 23. As the appeal scheme comprises an increase of 38 square metres of office floorspace, the contribution to the existing shortfall in space and the growth in jobs would be low. Additionally, there is little substantive evidence before me to demonstrate how the proposal would better support the needs of more modern working practices over and above the current accommodation. Nor has it been demonstrated that the propose would provide a more attractive offer when compared with other commercial spaces, including those I noted to be available for sale or lease nearby during my site visit. Any social and economic benefits from the construction and subsequent occupation of the proposal, including indirectly to local shops and businesses nearby, would similarly be at a low scale. 24.

20 Conduit Street, London, W1S 2XW — City of Westminster Council — Appeal Decisions Various environmental benefits of the proposal have been set out in the Sustainability Design Statement3 comprising the use of high-quality, durable materials, and a more efficient replacement plant. However, the scale of the benefits which would be derived from these elements has not been quantified given the low level of detail before me. 25. On balance, the totality of the benefits outlined above do not outweigh the level of harm identified to the special interest of the listed building or the significance of the MCA. Additionally, the continued office use of the appeal site is not dependent upon the appeal scheme. As such, clear and convincing justification for the less than substantial harm I have identified above has not been demonstrated. The proposal would fail to preserve the special interest of the Grade II listed building of 20 Conduit Street and the character or appearance of the MCA would be neither conserved nor enhanced. This carries considerable importance and weight, consistent with the statutory duty in the Act and reiterated within the Framework. 26.

20 Conduit Street, London, W1S 2XW — City of Westminster Council — Appeal Decisions Consequently, I conclude that the proposal would not preserve the Grade II listed 20 Conduit Street, or its setting, or any of the features of special architectural or historic interest that it possesses. Nor would it preserve the character or appearance of the MCA. Other Matters 27. My attention has been drawn to several other listed buildings located near the appeal site. However, as I have found that the proposal would not preserve the listed building, or its setting, or any of the features of special architectural or historic interest it possesses and the character or appearance of the MCA would not be preserved, it is not necessary for me to consider these other listed buildings further as it would not alter the outcome of these appeals. Conclusion 28. For the reasons given above and having regard to all relevant matters raised, I conclude that both appeals should be dismissed.

20 Conduit Street, London, W1S 2XW — City of Westminster Council — Juliet Rogers, INSPECTOR 3 Set out in a letter from Savills to the Council, dated 31 March 2025 https://www.gov.uk/planning-inspectorate 5