Hi Steve,
IIRC all the DBP GTI's were imports mate, a place in wigan called Ron Hodgson cars sold a couple a while back, usually highly specced and as you say the rarity factor of the colour makes them an attractive buy!
I'd just definately check the origin of the car and bid accordingly as if it is an import it could affect its resale value in the future, not a problem selling cheap if you buy cheap, but this one sounds a bit over book imo...
HTH