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Flat 1D Block 1 Portman Mansions Chiltern Street London W1U 5AJ

25/05866/FULLFull Planning Permission ApplicationRefused
Full

Refused on 17 October 2025

Council decision: Application RefusedDelegated (officer decision)

Approximate site (title boundary)
Boundary © HM Land Registry, © Ordnance Survey · details

This information is subject to Crown copyright and database rights 2026 and is reproduced with the permission of HM Land Registry. The polygons (including the associated geometry, namely x, y co-ordinates) are subject to Crown copyright and database rights 2026 Ordnance Survey AC0000851063. Conditions of use.

Proposal

Replacement of existing single-glazed timber sash and casement windows with double-glazed timber sash and casement windows to match the existing style and opening type. Existing window frames to be retained with no changes to the structural openings.

Received
19 August 2025
Decision level
Delegated (officer decision)
Ward
Marylebone
Agent
Design Extension - https://www.designextension.co.uk/
  1. Received19 Aug
  2. Validated1 Sep
  3. Consult.
  4. Target27 Oct
  5. Decided17 Oct

Decided in 46 days (council typically 49)

About this application

This is a full planning application for window replacement at Flat 1D Block 1 Portman Mansions Chiltern Street London W1U 5AJ. Westminster has handled 4,484 applications of this type. This one was decided in 59 days, 10 days longer than Westminster's typical decision time. The site is in the Portman Estate conservation area, with 3 listed buildings nearby. There has been 1 other application at this address. In the past year there have been 171 applications across Marylebone. We hold 1,070 applications in total for the W1U 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.Planning something similar? See what gets approved on your street

Application details

Postcode
W1U 5AJ
Application type
Full Planning Permission Application
Scale / size
Small

Planning application dates

Date validated
1 September 2025
Consultation expiry
8 October 2025
Target decision date
27 October 2025

Applicant and agent

Agent
Design Extension - https://www.designextension.co.uk/
Agent address
3 Great Woodcote Park Purley CR8 3QU

Planning decision

Statutory period
56 days

Publicity

Last advertised
17 September 2025
Advertisement expiry
8 October 2025
Site notice start
4 September 2025
Site notice end
25 September 2025

Additional information

Planning Portal ID
PP-14259976
Comments
0
Documents
13

Site constraints

Checking the site
2/3
Council recordsAppealsFlood risk

Designations that overlap or adjoin the site outline.

  • Conservation area: Portman EstatePart of the site
  • Article 4 direction: Article 4 Basement Development Permitted Rights Removed+1 more
  • Flood zone 1: Low probability (rivers and sea)
Also checked, none recorded (22)

flood storage 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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