This larva (c20mm) was found in the kitchen crawling up the window.
I put it in a pot with an Apple, Hawthorn and Birch leaf as part of an experiment to find an acceptable foodplant.
It was probably looking for a suitable place to pupate as it has spun the Hawthorn and Birch leaves together.
I think it is a species of sawfly, but I'll hang on to the pot and see if it pupates and hatches.
Meanwhile, if anyone recognises it please let me know.