Damn puncture. Might have got it pinched against a kerb or something Saturday night when parking up/leaving, but it went flat as a pancake and was instantly noticable as I drove away - but I dropped off the kerb immediately as I moved away so I didn't have any gap between moving or steering and noticing it to be able to say.
Still, I needed the car for Sunday so I couldn't leave it there and come back in the morning (early-ish start) to sort it out at leisure; besides, my mate was going out Sunday too. I'd had a good evening at his just hanging out with a few friends and playing games, so to be changing a tyre for my space-saver spare at 12.30am was not fun. Thankyou very much again for your help though, Jim. Half an hour later I drove home carefully and noticing the difference in grip; lighter steering; and tendency for the ABS to come on without anywhere near the normal amount of provocation. Not going to dare to push it's performance envelope like this.
I made it down to Lewes-way-ish and back again - 5hr drive there and back via picking a friend up without a problem luckily. Not an ideal trip to make on a spare tyre but it had been arranged weeks ago and I didn't want to let everyone down at the last minute. Gotta see if they can repair the tyre now, or if it's another £44 into that bottomless pit they call car maintenance (glad it was a cheap tyre).
PS: more posts coming soon, got a few lined up in draft.