My suspicion that my Nessie was a grass snake has ben confirmed. My son in law found a pic. of an immature grass snake which matched my visitor. At least it means there must be some of breeding age around fairly locally which is cheering news.
Another mystery resolved. If you have a working ie warm ,compost heap, its probably been a nursery this summer. (!) I recall a year when it was 'prudent' to lift the cover from mine with a dutch hoe,( having the longest handle in the shed) prior to filling allowing the residents time to disappear. I have an aversion to writhing serpents.
I can stop scratching that itch ! I have a compost heap but don't think it is very warm as it is just an open heap. I have never seen anything wiggly leaving it when I have started using it. I always had slow worms in the compost heap in my previous garden but they never bothered me.