Update ... well, it failed! Have to take it back in on Monday for relatively minor repairs and re-test. More the inconvenience than the cost that is the bother, sigh. I was actually quite hopeful when I walked back to the garage as the car was sitting outside and I had not had a phone call, but no such luck ...
How lovely to have someone sort you out all in one day. I was offered a slot tomorrow, but already have a commitment so had to defer to Monday. Still MOT only cost £26 and they are including parts for free for repairs, 'just' 2 hours of labour to pay for so could be worse.