I've got answers to 19 of them and they don't tally with some answers above!
The American President one is making me lose the will to live!
It's numbers 6 and 11 that I knew off the top of my head. I did know the Ruth Ellis one but had forgotten the answer.
Re the tube station one, Seven Sisters gets its name from a group of large trees. I'm not aware of there having been a pub of that name there. Of course, that doesn't mean there wasn't!