Bo, if you get a clear night
go up and visit the
Kielder Observatory, it's one of the (if not the) darkest places in England (note: there are darker, more remote regions in Scotland and Wales)
Then there's the
Royal Observatory in Greenwich which is worth a trip if you're in the area (it's been a few years since I last went).
If you were out in the west country, I'd suggest the Herschel museum in Bath.