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17 William Mews London SW1X 9HF

26/04409/FULLFullApproved

Approved on 18 September 2026

Site boundary (council red line)

Proposal

Variation of Condition 1 of planning permission dated 12 June 2025 (RN: 24/07507/FULL) for the erection of a roof extension and alterations to existing front elevation and fenestration; excavation of a new basement below part existing dwellinghouse; Namely, amendments to the ground floor windows.

Received
3 July 2026
  1. Received3 Jul
  2. Validated7 Jul
  3. Consult.
  4. Target
  5. Decided18 Sep

Decided in 73 days (council typically 49)

About this application

This is a full planning application for a new dwelling at 17 William Mews London SW1X 9HF. Westminster has handled 4,484 applications of this type. This one was decided in 73 days, 3 weeks longer than Westminster's typical decision time. The site is in 3 listed buildings nearby. There have been 3 other applications at this address. In the past year there have been 383 applications across Knightsbridge & Belgravia. We hold 1,285 applications in total for the SW1X postcode area.

86% of full applications at City of Westminster were approved. Across all application types, the council typically decides in about 7 weeks (median).

Based on decided applications received in the last 3 years.See what's approved near your address

Application details

Postcode
SW1X 9HF
Application type
Full
Scale / size
Small

Planning application dates

Date validated
7 July 2026

Site constraints

Checking the site
2/3
Council recordsAppealsFlood risk

Designations that overlap or adjoin the site outline.

  • Article 4 direction: Article 4 Basement Development Permitted Rights Removed
  • Flood zone 1: Low probability (rivers and sea)
Also checked, none recorded (23)

flood storage areas, conservation areas, listed buildings, tree preservation orders, green belt, scheduled monuments, World Heritage Sites, World Heritage Site buffer zones, registered parks and gardens, registered battlefields, Heritage at Risk entries, nutrient neutrality catchments, national parks, National Landscapes, SSSIs, Special Areas of Conservation, Special Protection Areas, Ramsar sites, ancient woodland, national nature reserves, local nature reserves, heritage coasts and brownfield registers.

A guide only, from official open data; it is not a planning search. Flood zones cover rivers and sea, not surface water.

Data © Crown copyright and others · sources and licences

Contains public sector information from planning.data.gov.uk (MHCLG and local planning authorities), licensed under the Open Government Licence v3.0. © Crown copyright and database right 2026.

© Historic England 2026. Contains Ordnance Survey data © Crown copyright and database right 2026. The Historic England GIS Data contained in this material was obtained on 2026-11-03. The most publicly available up to date Historic England GIS Data can be obtained from HistoricEngland.org.uk.

© Natural England copyright. Contains Ordnance Survey data © Crown copyright and database right 2026.

© Environment Agency copyright and/or database right 2026. All rights reserved. Flood Map for Planning, Open Government Licence v3.0.

Contains Ordnance Survey data © Crown copyright and database right 2026.

Source: Office for National Statistics licensed under the Open Government Licence v.3.0. Contains OS data © Crown copyright and database right 2026.

Source: Westminster

Contains public sector information from the Planning London Datahub, licensed under the Open Government Licence v3.0.

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