"TheScullster" wrote
Thanks to all for comments.
I'm inclined to think the consensus hedgehog is likely.
Will they tolerate a cat-ridden neighbourhood though?
If so, where am I most likely to catch sight of him/her? - Under the
shed? Back of the borders?
Our garden isn't huge (about 17m x 10m) but is a bit "natural" in
parts!

They can roam around quite a large area and may be visiting several
gardens in the vicinity at night. If your garden has a wilder area I'm
sure any self-respecting local hedgehog would gladly add it to its
nightly itinerary.

You'd probably be most likely to catch sight of one (or maybe
hear it first) if you go out after dark when they go grunting and
snuffling around in search of a meal. As for cats, I should think they'd
soon learn to keep well away from the spines of a hedgehog, but possibly
the young hoglets might be more at risk.

--
Sue