Thank you all, gents. And no, John, egg-sucking advice always well-received.
I did warm up, though possibly not enough! My squash partner never warms up properly and he did the same thing a year or so ago, so I am pretty careful about it. Could have been exacerbated by strenuous digging of leyladni roots earlier.
I do partake in fitness with the kids at judo, (though don't do the judo part), so am generally pretty fit, so feel a bit hard done by, but hey, as you guys say, it should heal OK as it's muscle. A mate snapped hi achilles a few years ago and he was in hospital for weeks then plaster and crutches for months - never want that injury!!
And max respect to anyone who is truly disabled, long term - I salute you