the best thing to do is ask around - local astronomers will know where the dark spots are.
you face an uphill battle in britain, but your best bets are out in the middle of nowhere, in places like cornwall, wales and scotland.
work with what you have. unless you live right in the centre of london or birmingham, it's always worthwhile to go out and have a look. you just have to adjust your expectations: forget galaxies and concentrate on planets and double stars and stuff.
