Leisure Trail: heard lots of negative stuff about those guys workshop skills.
Touratech are also worth avoiding at any cost including buying new bikes. Allegedly (for legal reasons) they have been known to strip out the high quality batteries and replace them with crap then charge £120 for a 'new' one when the bike develops problems, they have (allegedly) done / not done warranty work and then charged both the manufacturer AND the customer.
In the Midlands we really struggle for a decent off road shop.
I know Redline and SS-Racing are both good boys with expert workshops but don't know about anyone else.
RJS Superbike are a top workshop.