[dspillett]

It seems common up here (York) though the reaction varies. Some decline, some places drop the value in the top jar, some may even make a point of chatting to you to drink the drink if the are not busy (though that is fairly rare).

I expect it varies as much in London, but culture tends to follow people who then follow the culture they are used to - so you may just frequent places where not tipping that way is the norm by virtue of your preferences and circle of friends.