Unfortunately soccer is the one thing i abhor...
You should be able to get tickets from one of the football stadiums or soccer team websites, maybe try one of the local information bureaus when you get to london, they should be able to give you info on getting tickets.
As for Car museums, there's a bunch of car museums scattered over the country...There are dragstrips located at Santa Pod (Buckinghamshire)
and Shakespeare county raceway (stratford upon avon) There's racing of some sort on every weekend, it usually alternates between Rods,bikes and the ricer brigade..If you give me ideas of which weekends you will be here for i can give you a list of shows and locations..Although be aware that the weather in the UK has been CRAPPY for most of the summer,major flooding etc, so the drags could be a washout...

Is it just you or a few people coming over?? i.e kids etc too?
cuz i can give ya bunch of cool stuff to do with kidz etc too...