if you're going to london, visit the following:
the london eye, big ferris wheel with good views over london if you do it on a clear day.
tower bridge, amazing when it goes up.
big ben, the big clock in westminster
museums, natural history museum is quite good, but i don't know if you're interested in that stuff.
Lord's, the cricket ground, on the tube it's st. johns wood, and as you're a cricket fan it's well worth it, you could even buy yourself a framed copy of the ashes 09 test that was at lord's
there's loads of cool stuff, too much to list. if you're going to cornwall, try going via stonehenge, i don't know how far out of the way that is, but it's quite cool.