If you come the the UK, don't limit yourself to London. It's a sh*thole, and unrepresentative of the rest of the country. Head west, down to Devon and Cornwall, then north throught Wales to Cumbria. Head up to Scotland if you have the time, then on the way back stop off at York (this is compulsory). Don't bother with Stonehenge. Fit in places like Wells and Chester if you can.