Mentioned several times
Buckland Auction House (In alternate 2009)
London is the capital of England and the United Kingdom.
Once when Piper's potion created more smoke than expected in the attic, Phoebe joked "Welcome to London."
Among the past lovers of Prue's Cupid listed was "Eric in London."
In an alternate future which Piper and Phoebe visited, where Prue lived to see 2009 and was the owner of Buckland Auction House, the business had expanded its branch to Paris, Tokyo and London.
The pirates used the mystical fog to travel to London before going to San Francisco.