I graduated in Mech Eng. from the University of Hertfordshire many years ago. They had quite a decent Engineering Department back then, doing Aerospace & Vehicle too. Not sure what it's like nowadays, but does have the advantage of being just North of London, so easy to get to Dover.
Imperial College in London definitely has a good reputation. If you've got the grades Cambridge University is good of course (assuming they offer undergraduate Mech. Eng.?) and a nice city to live in.
Good luck with whatever you do, and good thinking posting on here. That wasn't an option when I was your age!
