I am sure you can fill in 9 hours in London easily.
But if you do find yourself near Borough Market/London Bridge area there is the George Inn in a lane across from the market. It is a 17th century where stables used to be as a coaching inn. Great place to have a drink if you are into history and not too tall to hit you're head on the roof.
Missed your message :( Yeah we had a great time, walked for more than 8 hours and have to say London is really beautiful. Love all the history and pretty cool pubs with all the black and gold. Also tried English breakfast :) Will be going another time to see more and this time with a plane instead of bus I was completely broken without sleep. :o