Moving the blind in our dining room today, I disturbed a winged insect, nearly 2 cm long, black and yellow but with a longer, thinner body than a "normal" wasp. (I have now released it into the garden, and didn't get a photo!)
It crawled around and flew a little, but it was slow and may have been hibernating?
We have quite a few trees at the boundaries of our garden, including a large Monterey pine, sycamore, ash, bay, & holm oak.
I wonder if it is some kind of wood wasp. It was mainly black, but there were some yellow parts.