Top Gear racing in a field - help!

[Rollcage]

A couple of years ago one of the the TG challenges ended up with the cars (Starion ,XJS and 635?) racing around in a field .This looked like a good cheap form of fun for a weekend ,can anyone shed any light on what it is and where it takes place around the country?

Its not Autograss ,but looked like an even cheaper more basic form of it.

Any guidance gratefuly received!

[zac510]

I remember the episode and that it was an 'endurance' race but apart from that I've got no idea..