A Google search shows an awful lot of other organisations using that address (n.b. should be WC1N, not W1CN), so I suspect it may just be a mailbox address.
It may be necessary for you to start by finding a geographical address for the business in order to stand a chance of finding a geographical phone number!
Also, is Fairfax Property the full and exact name of the business?  There does not appear to be a company called Fairfax Property Limited, so do you know if Fairfax Property is the trading name of another company, or is it a partnership or what?

Sounds like it's just his trading name; quite possibly the telephone service is not even in the name of Fairfax Properties.  No clues in the rental agreement I suppose? 
Otherwise, there is really little or nothing to go on to help in finding a geographical number I'm afraid.