Thanks Pav.
Liz, I know you're experienced in a rural area, but I'll be honest - most of the people round here wouldn't keep their cats in even if I asked. Also, even if I trapped him at 5 in the morning, I have nowhere to put him so that's not plausible. I've asked a friend to borrow her big dog crate because that's the only solution I could come up with. I'll happily get up throughout the night and check a trap, but if there's nowhere to put him it wouldn't really work.....
Our cats were kept in until about 2 to give me a chance and then I opened the cat flap. Off to bed, will be setting the trap fairly early tomorrow to try again.