My wife and I stayed a few days in London at the Marriott across the street from Speaker's Corner in Hyde Park. We went out for fish and chips and a pint at a local pun the doorman suggested. It was right across the street from Purdy's. Too bad they were closed. I would take one of the bus tours of London where you can get on or off wherever you want. The Guards Museum by Buckingham Palace and the Horse Guards Museum by Trafalgar Square are also interesting.
Don't get caught with a lockblade pocketknife. They have no sense of humo(u)r.