I recently had difficulty loosening the lockring on a cassette. So this am after the torch relay I popped down to Newtongrange to the Lothian Bike Shed to see if they could help. The guy there was very nice and did it embarrassing easily (though using a vice - must get one) and for free.
The last time I went there, they were based in Dalkeith and he gave me some cable end thingies for free. So at the moment I can't recommend them enough and I will be trying them out again. They seem to be mainly mechanics rather than retail. I asked about the price of wheel building - £ 20 for labour - you bring your own rim/hub.