I was there too
The car is a Ford Maxxum GTP, see here (
http://www.philstott.co.uk/carswesupport.html) - that's the website of the guys who were running it.
The paint scheme is not authentic for a Maxxum as far as I know, but it was run by Roush Racing in the day.
There are a few other cars in the historic GTP/GrC series which don't run anthentic colour schemes. The yellow FromA Nissan has got black stripes down either side of it for example..