According to the Ordnance Survey, who've made available a huge OS Open Names dataset, there are 43,120 "populated places" across Great Britain. I wondered how many places there were in London so I downloaded a small subset of the data, and according to the Ordnance Survey there are 681. They range from cities like Westminster to hamlets like Bopeep, taking in Suburban Areas (like Neasden) and Other Settlements (like Penge) along the way. There's more about the dataset and some of the fancy cartographic stuff you can do with it here, courtesy of AlasdairRae.
According to the Ordnance Survey London has no towns. Several exist just beyond the boundary, including Potters Bar, Dartford, Westerham, Esher and (er) Chigwell, but the OS don't use the 'town' category within the capital.
London's 3 cities: London, City of London, City of Westminster London's 25 villages: Berry's Green, Botany Bay, Chelsfield, Coldblow, Crews Hill, Cudham, Downe, Harefield, Hazelwood, Hill End, Horns Green, Keston, Leaves Green, Luxted, Malden Rushett, Maypole, North Cray, North Ockendon, Pratt's Bottom, Ruxley, Single Street, South Harefield, South Street, Upper Ruxley, Wennington London's 8 hamlets:Bopeep, Edgware Bury, Farthing Street, Hockenden, Kevingtown, Nash, Newyears Green, Rowley Green
I like the definitiveness of these three lists. I also knew where most of the villages and half the hamlets were without having to check on a map. Editors of listings magazines and marketing departments for housing developments should note that Marylebone, Notting Hill and the Greenwich peninsula are not villages.
The first 5 places in alphabetical order: Abbey Wood, Acton, Acton Green, Addington, Addiscombe The last 5 places in alphabetical order: Worcester Park, World's End, Wormwood Scrubs, Yeading, Yiewsley
The most common first letters for London placenames are S (81), C (71), B (69), H (67) and W (61).
The 4 places that start with I: Ickenham, Ilford, Isleworth, Islington The 3 places that start with V: Vale of Health, Vauxhall, Victoria The 2 places that start with Y: Yeading, Yiewsley The only place that starts with Q: Queensbury
No London placenames begin with J, X or Z.
Placenames including the letter J: Clapham Junction, St James's, St John's, St John's Wood Placenames including the letter X: Alexandra Park, Bexley, Bexleyheath, Brixton, Hoxton, Loxford, Luxford, Old Bexley, Roxeth, Ruxley, Upper Ruxley, Uxbridge, Uxbridge Moor, Vauxhall Placenames including the letter Z: Fitzrovia, Freezy Water, Furzedown, Hazelwood
There are 50 places called Something Park, 33 called Something Green, 31 called Something Hill, 12 called Something Heath, 11 called St Something, 11 Upper Somethings, 8 Lower Somethings and 6 called Something Wood.
London's longest placename is Hampstead Garden Suburb which has 21 letters. In second place is Enfield Island Village (20) and in joint third are Carshalton on the Hill and Northumberland Heath (19). Residents of Barking Wharf Square, Frank Whipple Estate, Kingston upon Thames and Richmond upon Thames share fifth place.
Seven placenames are used in two different parts of the capital.
Because this is an Ordnance Survey dataset it can also do geographical extremities.
London's most northerly places: Crews Hill, Bullsmoor, Botany Bay London's most westerly places: Uxbridge Moor, Hill End, Longford London's most southerly places: Old Coulsdon, South Street, Kenley London's most easterly places: North Ockendon, Cranham, Upminster
When it comes to names with compass directions, West wins with 18 West Somethings. South is next with 16, then North with 12 and finally East with 8.
The five boroughs with the most places: Bromley (58), Barnet (40), Hillingdon (32), Enfield (30), Croydon (27) The five boroughs with the fewest places: City of London (1), Barking and Dagenham (9), Kensington and Chelsea (9), Hammersmith and Fulham (11), Islington (13)
All other boroughs have between 16 and 26 places.
The postcode areas with the most London places: E (75), SE (65), N (62), SW (62), BR (49) The postcode areas with the fewest London places: WD (1), EC (4), TN (7), WC (7), KT (19)
The only London place in the Watford postcode is Elstree Park (WD6).
3 of London's newest places: Barking Riverside, Barking Wharf Square, Hallsville Quarter 4 places in Tower Hamlets I'd never heard of: Coalmakers Wharf, Festubert Place, Frank Whipple Estate, Hitchin Square 5 other places I'd never heard of: Bandonhill, Cowley Peachey, Maitland Park, Risley Close, Tavern Quay