Business in London
Details the trading hours of banks, businesses, shops and government offices.
http://www.london-guides.co.uk/chapter/bw1/b0101010.htm

Fodor's
Lists the trading hours of gas stations, banks, shops, etc.
http://www.fodors.com/miniguides/mgresults.cfm?destination=london@91&cur_section=tra&pg=3

Visit Britain
Covers opening hours and other hints and tips on shopping in the UK.
http://www.visitbritain.com/in/fact_files/advice/shopping.htm

Visit London
The local business hours explained.
http://www.visitlondon.com/html/index.php?pgd=59&rcd=163