On Saturday the snake reappeared and climbed on top of a juniper bush, hoping for some sunshine.
Then it headed over to the birdbath, perhaps hoping to find a frog.
Yesterday another one appeared, right outside Cherry's back door. It was longer and fatter than the first, so possibly a female. It also had more prominent yellow and black markings around the neck.
Sadly, the grass snake is a species that doesn't get this far north. This distribution map is from the Amphibian and Reptile Conservation Trust website. (The northern outlier data points on the map are very dubious.)
Compare it with the distribution map for adders,
One interesting difference is that grass snakes lay eggs whereas adders give birth to live young. Another is that the grass snake allowed Cherry to get quite close (0.5m) to take its photo. If it senses she is too close it freezes (which helps with the photography) whereas an adder would slide away if it felt threatened.
Many thanks to Cherry for the photos. With photos like these I think she needs to start her own blog.