Internal alterations by area

Two separate approval systems. Confusing them is the most common — and most expensive — mistake in domestic building.

Building regulations are a separate system from planning — and the certificate at the end is the one your buyer's solicitor will ask for.

Almost every London extension, loft and basement engages this Act. Here's how it actually works.

NW1 runs from the Nash terraces around Regent's Park through Camden Town to Somers Town.

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.

N1 covers Barnsbury's Georgian squares, Canonbury's villas and, over the Hackney boundary, De Beauvoir Town.

E8's Victorian terraces around London Fields and Graham Road are among the most actively extended in London.

N4 meets three boroughs — Haringey, Islington and Hackney — around Finsbury Park, so identical houses a street apart can answer to different planning departments.

SW3 is the heart of old Chelsea — the Cheyne, Chelsea and Royal Hospital conservation areas run down to the river, with Hans Town reaching into Knightsbridge.

W6 runs from the Brook Green and Hammersmith Grove conservation areas to the riverside at Crabtree and Fulham Reach.

SE1 is Southwark's listed riverside — the Borough High Street, Bermondsey Street, Tower Bridge and Trinity Church Square conservation areas, much of it statutory-listed.

SW4 is Clapham's Victorian terrace heartland — the Clapham, Clapham High Street and Abbeville Road conservation areas around the Common.

E1 holds the borough's most significant heritage — the Fournier Street, Elder Street and Artillery Passage conservation areas of Spitalfields and the Wapping Pierhead and Wapping Wall waterfront.

SW18 covers the Wandsworth Town, Magdalen Park and Old Devonshire Road conservation areas and the Victorian 'Tonsleys'.

TW9 covers Central Richmond, Richmond Green and Richmond Riverside, and at Kew the Kew Green and Kew Gardens conservation areas around the Royal Botanic Gardens — a World Heritage Site.

NW11 contains Hampstead Garden Suburb — one of the most complete planned suburbs in the world, where conservation designation, an Article 4 direction and the Hampstead Garden Suburb Trust's scheme of management all apply, so external alterations need both planning permission and Trust consent.

W5 is the heart of the 'Queen of the Suburbs' — the Ealing Common, Ealing Green, Mount Park and Creffield conservation areas, the Hanger Hill Garden Estate and the pioneering Brentham Garden Estate at Pitshanger.

SW19 spans Wimbledon Village, Wimbledon West and Wimbledon North — the borough's most tightly controlled conservation areas — and the John Innes estate at Merton Park, whose conservation areas carry old-style Article 4(2) directions removing most permitted development.

KT1 is the royal borough's core — Kingston Old Town, Riverside South, Grove Crescent and the Fairfield and Knights Park conservation areas.

BR1 covers Bromley Town Centre and the leafy Sundridge Avenue and Mavelstone Road conservation areas towards Bickley.

HA1 centres on Harrow on the Hill — the Village, Harrow School and Harrow Park conservation areas, with Roxborough Park nearby.

NW2 takes in the Mapesbury and Willesden Green conservation areas — handsome late-Victorian villa streets where, as across Brent, conservation areas carry Article 4 directions removing permitted development.

SE10 is the Maritime Greenwich World Heritage core — the Old Royal Naval College, Queen's House and Royal Observatory — wrapped by the West Greenwich, East Greenwich and Ashburnham Triangle conservation areas, several with Article 4 directions.

SE4 is the Brockley conservation area — one of London's largest Victorian conservation areas, with an Article 4 direction removing permitted development, so windows, doors and roof changes need consent.

EN2 is the borough's historic heart — Enfield Town and the medieval Gentleman's Row, the Forty Hill and Clay Hill conservation areas, with Forty Hall and Green Belt beyond.

E17 is Walthamstow — the historic Walthamstow Village conservation area (St Mary's Church and Orford Road), Lloyd Park and the Bakers Arms, plus Wood Street.

SM1 covers Sutton town centre and Benhilton, the borough's busiest district.

CR0 spans Central Croydon and the Victorian streets of Addiscombe and Waddon.

DA5 is Old Bexley — the historic village conservation area on the Cray, with Hall Place nearby and North Cray Village beyond.

W4 is Chiswick — Bedford Park (often called the world's first garden suburb, with an Article 4 direction), Chiswick House, Old Chiswick, Turnham Green and Strand on the Green.

UB10 covers Hillingdon village and eastern Uxbridge — the Hillingdon Village conservation area among them.

IG1 is Ilford — the borough's commercial heart, with Valentines Mansion and its park among the conservation set pieces.

RM1 is Romford — the historic market-town core and conservation area at the borough's centre.

E15 is Stratford — the Olympic legacy, the Stratford St John's conservation area and the industrial heritage of Three Mills and Sugar House Lane nearby.

IG11 is Barking — the Abbey and Barking Town Centre and Abbey Road and Riverside conservation areas around the abbey ruins.

EC2 holds the City's main residential community — the Grade II–listed Barbican and Golden Lane estates, within the Barbican and Golden Lane Conservation Area — alongside Bank, Guildhall and Moorgate.