Agree that it's very strange he would be asking you to travel to London... I understand someone from an area with not a lot of prossies having someone come a long way, but London? if you can't find what you want here, then you don't want anything!
I would take the train, why drive? Ask him to buy your tickets for you, then add some shit for extra expenses which you need up front... and yeah, you're not charging enough. But really, I would be hesitant...