Someone was telling me about a place called 'Mikecanic' in Cheshire that tunes rally cars... but I don't know anything more about them than that (google give me nothing).
EDIT: I lie -
this is them... is £35 good for a power run on the rolling road? What about £60 for the first hour of tuning on it? That seems quite cheap to me, but I haven't ever been on one so don't really know.
I agree with Geoff though... unless you need the car mapped or something like that, a local garage that you trust can do anything you want for a much better price.