After the race, I decided to head off to the pits to try and get a look at the cars, no chance there, they are all locked up tight within minutes of the end of the race unless you have a special pit pass.
On the way to the pits, I came across this Lister pump unit, and saw several more of them around the track. For the life of me, I cannot think of why they would want them at the GP - it is not as though it is big enough to empty the lake in an emergency.
Anyway, onto the important bits, it seems to be a Lister LD-3 or ST-3 (they both look the same to me) direct coupled to a huge pump (the hose was about 15cm/6 inch bore and looked like it could handle some serious pressure. The unit was electric start and painted in the colour of "Coates Hire" the company that owned them. I guess it might make a change from green if you wanted to restore one this way.
I was quite interested to see these engines ready for actual use instead of pumping water from one barrel to another at a show. Unfortunately I could not get close enough to read or photograph the serial number and makers plates (although "Lister" is prominently stamped into the castings in quite a few places). The engine is basically the same as my Lister LD-2 on my Autotruck except that the exhaust and air filter don't seem original (unless Lister did them this way later).