Thanks for the advice and thoughts, I'll keep you updated.
I would prefer Xavier to be on a good quality dry food but he hasn't been keen on what I've tried him on so far.
Sunny is a dry only cat (apart from when she enquires if there's anything going) she is on James Wellbeloved Senior/Light which is a very popular hypoallergenic dry food in the UK.
I'd like to get him onto a dry food really, it's a matter of finding one that he finds palatable.
He's on Felix pouches at the moment, and I have to admit he seems to be worse on these than when he was on Whiskas pouches.

I'll keep you updated on him.

Thanks