Bug Bog.com
Offers links to the websites of major embassies in London.
http://www.bugbog.com/directory/embassies/embassiesuk.html

Foreign & Commonwealth Office
Click on the appropriate link to search for British embassies overseas.
http://www.britishembassy.gov.uk/
http://www.fco.gov.uk/

Home Office
Index of foreign embassies in the UK. Just click on the appropriate link to access the list.
http://www.homeoffice.gov.uk/
http://www.ukvisas.gov.uk/

Limey Search
Provides links to major British embassies abroad.
http://www.limeysearch.co.uk/Government/International_Affairs/British_Embassies_Abroad/

Travel London
More links to embassies in London.
http://www.travellondon.com/templates/Londontips/Embassies.html

UK Visas
An official guide to the country's entry regulations.
http://www.ukvisas.gov.uk/
http://www.homeoffice.gov.uk/