As of 2015, a top resource for London phone numbers is White Pages UK, the official telephone directory of England. To search residential London phone numbers, enter a name and location into the search bar on the home page, then click Search.
A resource for London business phone numbers is the Yellow Pages on Yell.com. In the search bar, enter the name or type of business you want to find, then a city, town or postcode, and click Search.
The BT phone book is another resource for business phone numbers listed in London. It does not contain residential phone numbers or cell phone numbers.