Garden room in Westminster

Usually a full application — and on a mansion-block flat, often not available at all.

Usually a full application on a house, and typically not possible on a mansion-block flat.

Yes — a full planning application under Westminster's basement policy, and on the area's many listed villas, excavation is usually ruled out.

St John's Wood is heavily listed, so there's a real chance your property is — and if it is, listed building consent is required for works affecting its character inside and out, on top of planning permission.

For most of Maida Vale, an external extension isn't really the question — the area is dominated by purpose-built mansion blocks, which are flats with no permitted-development rights, so works are internal and governed by your lease as much as by planning.

In most of Maida Vale, a loft conversion isn't available to you — the mansion blocks are flats whose roofs are common parts owned by the freeholder.

On Maida Vale's mansion blocks, a private basement generally isn't available — the structure is shared and the ground belongs to the freeholder.

Parts of Maida Vale are listed — including some of the mansion blocks and stucco terraces — and if your building is, listed building consent is required for works affecting its character inside and out, on top of planning permission and (on a flat) a freeholder licence to alter.

Almost certainly not as permitted development — and on the Nash terraces, an external extension is usually off the table entirely.

On the Nash terraces, effectively no — roof alterations to a Grade I-listed composition are not the kind of change that gets consent.

On the Grade I-listed Nash terraces, excavation is protected against almost absolutely — a basement is generally not available.

Most of Regent's Park's residential terraces are Grade I-listed Nash architecture, so listed building consent is the governing permission — required for works affecting the building's special character inside and out, in addition to planning permission.

W1 carries some of the densest heritage protection in the country — Mayfair and Marylebone's estate-managed Georgian streets are conservation areas wall to wall, with a high share of listed buildings.

W2's white stucco terraces around Bayswater and Lancaster Gate sit largely in conservation areas, with many buildings converted to flats — which removes permitted development rights entirely.

W9's mansion blocks and canal-side villas in Maida Vale and Little Venice are heavily conservation-protected.

SW1 spans Belgravia's Grade II* stucco squares, Pimlico's grid of listed terraces and the political core around Westminster itself.

NW8's villa stock — Italianate, detached and semi-detached — is unusual for central London and gives more scope for extensions than terraced districts.

WC2 is theatreland and Covent Garden: dense, heavily listed and almost entirely conservation-controlled.

SW1E is Victoria: office-led and largely commercial, rebuilt along Victoria Street and Bressenden Place in glass and stone around the station approaches.

SW1H is government Westminster — ministries, the Broadway offices and the streets between St James's Park and Victoria Street.

SW1P runs from Westminster Cathedral and Horseferry Road down to Millbank and the Smith Square streets.

SW1V is Pimlico proper: a white stucco grid of mid-nineteenth-century terraces, nearly all long since divided into flats, alongside the post-war blocks of Churchill Gardens and the interwar development at Dolphin Square.

SW1W covers the southern half of Belgravia — Eaton Square, Chester Square and the Ebury Street and Elizabeth Street grid — thinning into commercial ground around the coach station and the Victoria fringe.

SW1X is Knightsbridge and the grand northern half of Belgravia — Belgrave Square, Lowndes Square, Sloane Street and the Brompton Road frontage — running to the Kensington and Chelsea boundary on its western edge.

SW1Y is St James's — Pall Mall, Jermyn Street, the Haymarket and Carlton House Terrace.

W1B is the Regent Street and Portland Place spine: flagship retail, hotels, embassies and institutional headquarters, with only a thin residential layer of upper-floor flats and the blocks tucked behind the main frontages.

W1C is Oxford Street itself, the stretch running west from Oxford Circus towards Marble Arch: department stores, flagship units and the offices above them.

W1D is the heart of Soho — Wardour Street, Old Compton Street, Dean and Frith Streets, and Gerrard Street in Chinatown.

W1F is northern Soho — Berwick Street market, Broadwick and Poland Streets, Great Marlborough Street and the Carnaby blocks.

W1G is the medical quarter: Harley Street, Wimpole Street and Devonshire Place, where uniform Georgian and early-Victorian terraces have been given over largely to consulting rooms and clinics.

W1H is Marylebone west of Baker Street towards Marble Arch: Gloucester Place, Seymour Place, George Street, and the Bryanston and Montagu Squares behind Edgware Road.

W1J is southern Mayfair — Piccadilly, Berkeley Square, Curzon Street, Park Lane and the Shepherd Market lanes.

W1K is northern Mayfair: Grosvenor Square, Mount Street, Park Street and the red-brick and Portland-stone terraces around them, with a network of mews behind.

W1S is a commercial district first: New and Old Bond Street, Savile Row, Conduit Street and Hanover Square — luxury retail, tailoring, galleries and offices, with a modest residential population in upper-floor flats and a handful of converted buildings.

W1U is Marylebone Village — the High Street, the kink in Marylebone Lane, Thayer and Blandford Streets, Manchester Square.

W1W is Westminster's slice of Fitzrovia — Great Portland Street, Great Titchfield Street, Hallam Street and Riding House Street.

WC2E is Covent Garden: the Piazza and market building, the Opera House on Bow Street, and Long Acre.

WC2N runs from Trafalgar Square through St Martin's Lane and Villiers Street down to the Adelphi and the Embankment.