Thanks all. Well as I said it was running Ok when we got home.
Anyway, I cleaned the electrical plug to the throttle body and checked that it's a smooth action. In the electrical box on the bulkhead I've re-seated all fuses and relays. I will replace those relays. All the fuses needed shoving in half a mm, so that's a worthwhile check. My fuse diagrams have boxes A and B reversed, that's quite common on the GDI. The fuse listings for each box start top left, come down the left bank, then across to the right and up the right bank. Worth knowing.
I also re-seated the two main fuses.
Then I cleaned the MAF sensor. It starts and runs perfectly in the garage..................So we'll see what develops