I did manage to find a couple of newspaper articles about the meeting that clearly refer to Clearly-Baker's speech, although neither of them mentions leys in any context:
http://ufo-warminster.co.uk/clippings/t ... ing_65.pdf
http://ufo-warminster.co.uk/clippings/c ... tement.pdf
Of course, it's possible that any mention of ley lines was omitted from the newspaper reports - perhaps they thought that one weird topic was enough to cover without mentioning ley lines - but surely they would have mentioned possible terrestrial connections if they had been discussed?
There is a tantalising quote from Arthur Shuttlewood's book The Warminster Mystery here:
Leys, but alas, no lines.Some evidence that Shuttlewood was outside of the ufological mainstream before his own sighting is given, perhaps, in The Warminster Mystery, where he asks, 'Have you heard of "leys" or "orthoteny"? I had not until Gavin Gibbons, an author, came to see me on 29th October, 1965.'