TheScullster writes
Thanks to all for comments.
I'm inclined to think the consensus hedgehog is likely. Will they
tolerate a cat-ridden neighbourhood though?

Yes. Cats tend to treat them with caution.

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're active at night, but they don't have a settled routine. So it's
a matter of luck when and where you see them. If you want to try feeding
him, a special tin of hedgehog food from the pet shop, or cat meat (meat
not fish based). Make a sort of box or tunnel with the entrance too
small for a cat and put the meat inside that. For added fun, cover a
piece of card with aluminium foil and gold it in the smoke of a candle
flame until it's completely covered with soot. Put this under the meat,
and n the morning you will see the tracks of anything that's visited in
the night.

--
Kay