The fact that you're only concerns regarding Imperial is the workload and the lack of campus life make me think you should go there.
Workload - Well if you've got/get the grades then you'll be fine providing you put in the work!
Lack of Campus - This ones a bit more difficult, but you named a whole list of great things about London that can make up for that, it is a great place to live.
Word of warning, London really is expensive, and unless you're parents are going to help you out a bit you're going to need a summer job. You get a bigger loan in London, but the costs are far greater and a house relatively central (zone 2 say) still costs alot. I wouldn't recommend a job during term because a) workload b) social life. Even if you live in the outer zones the cost of commuting seriously adds up. This shouldn't be something to put you off Imperial, it's a great uni, just something to think about!