just want to close this thread with some news
a friend of mine works in a breakers yard in leek, a 90bhp GP came in late august and it had a tuning box, he nabbed it for me.
I fitted it yesterday, there are a few settings [its set to sort of middle - power/economy]
already, the difference is quite substantial, the lag that I was suffering has come right down, so its more driveable especially pulling away, power throughout seems perkier
doesnt make any smoke, which pleases me.
done around 100 miles on it today on a variety of road types, its just a much better car.
got my MOT in a couple of weeks, will see how it does.
end of the day, it was free, and it can be taken off as easily as it was put on.