Question Author
Greetings each.
I thank you all for your responses.
Mr Fickens has likely provided the answer, although I am still keeping an open mind.
The cat concerned has, from time to time over the past 12 months, nibbled at his cat litter and has recently taken to licking the new concrete BUT:
None of this activity is regular so I am just monitoring the situation at the moment as he hasn't done any of it for a couple of days or so.
He eats well, although he also likes a saucer of milk each day. To all intents and purposes he is just a normal cat, if a little over-active from time to time, although he has been a bit of a "bull in a china shop" ever since I acquired him just over a year ago.
His former "trustee" told me he had been fed a lot of curry stuff and had a bad skin condition as a result. That I can vouch for, although his skin condition has now almost disappeared since I started feeding him normal cat food.
If anything changes I shall get back to you all. In the meantime, thanks for all your helpful suggestions and 'jonnyboy12's wit!
Be good!
Cheers.