Luckily, by the still hot temperature of the pork joint that was cooking, it hadn't been out very long. A quick furtle showed that the fuse for the electrics had gone. (I'm still bemused by a gas oven needing an electricity supply). With the new fuse in place our evening meal was back on schedule.
I'm now full to the brim with pork, roast potatoes, peas, carrots, green beans and Jane's dellicious gravy.
[A little later I noticed that the light in the oven isn't working; the culprit has been found]