St. Barnabas Church: http://www.stbk.org.uk
This is an Anglican church in Kensington, representing over 15 nations. Prayer timetable is online.
Bloomsbury Central Baptist church: http://www.bloomsbury.org.uk an international place of worship.
The Buddhist Society: http://www.thebuddhistsociety.org will give you all the details you need. There are many Buddhist temples dotted in and around London, among which is the first Thai Temple in London: http://www.buddhapadipa.org
Roman Catholic Diocese of Westminster: http://www.rcdow.org.uk Very central, near Big Ben and Victoria.
Hindu Council UK: http://www.hinducounciluk.org, there is a large Indian population in London and you will have no problem finding a Hindu temple.
East London Mosque and London Muslim Center: http://www.eastlondonmosque.org.uk
This mosque offers services and a center where you can find books in English, Arabic, and other languages. Prayer timetable is online.
London Jewish Cultural Center: http://www.ljcc.org.uk
Learn Hebrew or find a synagogue in your area.
In the heart of London, visit the Westminster Methodist Central Hall : http://www.methodist-central-hall.org.uk for more information and other places of worship.
The Religious Society of Friends can be found just north of central London in Bloomsbury http://www.quaker.org.uk