Graham I agree a need to be careful, and I hope that anyone reading this noted that I am not a lawyer, so should not take anything I say as legal advice.
From Art and Copyright (2nd Ed), Simon Stokes, 2012, ISBN 9781849461627:
"The protection of utilitarian or mass-produced items by copyright was an important and controversial feature of UK copyright law until the CDPA. In particular, as copyright protected engineering drawings of product designs as graphic works, this copyright would protect against indirect copying of the drawings through copying the products in question. The effect of the CDPA was to exclude the vast majority of industrial designs from copyright protection. This was done by effectively removing copyright protection from designs other than for artistic works and typefaces ... In short, the intention behind the CDPA was to leave copyright as the preserve of of what might properly called artistic works."
Simon Stokes happens to be a partner at our solicitors, so we could probably get a definitive answer for a couple hundred quid if we have a whip round