Launched in 1996 by the publishers of the Yellow Pages directory - its famous yellow book was one of the first business directories ever created. yell.com lists the names, addresses and telephone numbers of over 2.9 million UK businesses.
Google My Business: the official business directory of Google. Being listed here means your business data (phone, address, opening hours etc) is dialled directly into the Google search results.
120,000 businesses listed, 1.6 million views per month. Businesses, sole practitioners, and anyone doing business with a physical address can add their listing for free.