Took it round the block to see what happens and all the controls did what I expected, except for the accelerator, which seemed to increase the noise made by the engine but had little effect on actual speed. Anyhoo, gathered up the passengers, who just about had a seat each (in the end I only had 8 people wanting lifts 'cos Iain is taking a bunch down tomorrow). Then we roared off into the sunshine. Van's don't have air conditioning, but they do have windows. Very hot. The van had a fan, but it was more about making noise than doing much useful (bit like the engine in this respect) so we opened the windows and thereby slowed the mobile greenhouse down even more.
The good news is that we got where we were going in the end, and by the finish I was getting quite adept at spinning the van round and fitting it into parking spaces. But I've not tried any handbrake turns yet.