At last... I've sorted out the watering system for the greenhouse, and now have a dripper hose connected to the water butt up at the allotment. I'll be very interested to see how it keeps everything going.
So it's all systems go for transferring my poor overgrown tomato plants from the home greenhouse, where they've been getting increasingly drought-stricken and pot-bound, to the luxurious quarters of the allotment greenhouse. Because I've got a whole greenhouse devoted to toms this year, I've been able to go to town on the varieties: I'm growing good old Gardeners' Delight for general use, then San Marzano, the "only" cooking tomato according to some - it's a plum variety and very reliable; and then Brandywine for massive beefsteak tomatoes for salads.
Brandywine can be quite tricky as you need to get the watering just right to avoid blossom end rot and all sorts of other difficulties: last year I only got a couple of edible ones, and the rest split and went to waste. But this year I've got my watering system, and anything is possible...!!