This is the place.
http://www.highcroftracing.com/company.htm
Chris found the link and was going to go see the cars/take photos for us, but then was told that the owner didn't want any visitors.
The photos you found are great, but would be even better if we could be certain which cars those were.
From the tiny photo on their website I thought that the Gulf GTR would be #12R, but now that appears to be incorrect. This should be #15R then I guess. We saw a gallery of photos of this exact GTR back in 2003 next to a light blue TVR Cerbera (possibly Beckham's?) in the UK, but that was the last time it has been spotted.
For the FINA car, my initial suspicion was #23R which was for sale in Germany when I heard about these (since there was no photo), but that car wears the race #9 and has driver's Kox and Ravaglia on the doors with white mirrors. The one that BMW takes around is also different, wearing #42 on its flanks. Both GTR #21R & #26R wore race #8 so it's really anyone's guess between the two of them.
>8^)
ER