It depends what you like really - but no, not really anywhere in the UK have them available to test.
The only places that may have them would be Overclockers (Stoke-on-Trent), then maybe Scan or Aria in Manchester, but they're probably too far to go.
Other than that - you could exploit amazon's return policy. But something, try it for a day then send it back if you don't like it?
The other option is a side called qwerkeys:
http://www.qwerkeys.co.uk/shop/index.php?route=product/category&path=67
You can get individual switches to try out, although it's not really replicable to a full keyboard, but should give you a little feel for the differences. Check keyboard availability first though - not really much point buying one of the white switches as you'll struggle to find a keyboard.
As for which are the best - it depends what you're doing. The Corsair keyboards use Red switches, which are regarded as the worst, but they're still a lot nicer than non-mech. Browns, blacks and blues seem to be the favourites.