Not sure if anyone has heard of Terraclean (http://www.terraclean.co.uk/) - a process that strips out carbon deposits from the engine, reduces emissions, improves MPG, so the manufacturer claims.
Anyway, a colleague has had it done to his Celica after it failed the MOT emissions, and raves about it. He says the engine is much more responsive, a massive difference. I’ve not had my 5 done yet, but after standing around for most of the winter I’ll probably get it done in the spring.
The garage I use for servicing and other bits of work now offer the Terraclean service, Scotlands Ash (http://www.scotlandsashgarage.co.uk/). The service is £90 + VAT.