I can 100% recommend Bromspec:
http://www.bromspec.co.uk/
I have no connection with the firm other than being a customer for about 6 years. Great guys, all ex-BMW, really know their stuff, use genuine parts and prices are fair.
Also had a bit of work done by Iridium:
https://iridiumengineering.co.uk/
Don't know them well, but they seem to know their stuff.