I asked this same question. BJV engineering (01442 834169), were recommended by somebody on here. There just off the M25 nr Kings Langley.
Cost me £160 to get my Alpina's refurbished, included the centre caps. Very good value and fantastic job of the wheels. If I was super critical, the painting on the centre caps was slightly lumpy, you can't see it on the car though.
Another 5star report for BJV, they did my wheels perfectly 2 years ago and they're still as new. I stripped the centre caps down to the metal rings and they painted those too for free.
My out of round RD wheels are now roundish (well they don't shake your kidneys about) and are a good quality finish. Not to forget the 170 all in for 4 x17 wheels refurbed and powdercoated in silver. (They didn't do any wleding or anything, just cleaned the face up. The rear has a few dents etc, but they're rounder than they were, hold air and dont vibrate.