I don't know anyone in NW of london, but I do know someone on here who is a mk1 guru for servicing and his based in SW of london...
richandhazel is his name on the site - Richard of course real name...
Give him a ping on here, you won't go wrong with Richard servicing your MK1, he has already serviced and fixed another members mk1 and they where VERY happy with the work done....
Hope this helps.