I really like the idea of foraging but I'm new to this country so not confident about what plants, mushrooms, seaweeds etc, are good for taking. Can you recommend a good guidebook, particularly for use in Scotland?

These have been recommended over on the official River Cottage forum when others have asked a similar question.

Food for Free by Richard Mabey

Wild Food by Roger Phillips

Mushrooms: River Cottage Handbook No.1

there is also some good info in A Cook on the Wild Side by Hugh Fearnley-Whittingstall, which has been reprinted and is available again over on the River Cottage website.