Motech Performance are only up the road at Huxley Cl, Wellingborough.
Not sure if they can do the work you need doing but they know there way around BMWs, take a look on youtube at the work the do. Seach motech on youtube and they also have a website.
http://www.motechperformance.net/
https://www.youtube.com/user/motechm...able_polymer=1