Help me find this book?

[ItsAllGoingToBeFine]

I know the Mumsnet hive mind is really good at this

Scottish (?) book. Written a while ago. Man leaves civilisation because of possibility of war? Maybe nuclear war? Lives alone in cave in I think Scotland, living off the land. I think it was quite a thin book, and may have been some sort of classic? Fiction I think?

I'm keeping my fingers crossed - it's been driving me mad trying to find it!

The Old Man of Lochnagor, written by Prince Charles?

No it wasn't that, but thank you for replying!

Typically, after months of intermittent searching, and after finally asking on MN I have found it . I must have finally hit the magic combination of keywords.

It was "Wild Harbour", by Ian MacPherson.