Thanks for all the replies

Our Birman is 3 and has been castrated quite a long time ago. We did consider getting him a playmate but that is really the last option as as I am 6 months pregnant we feel it would be easier to look after 1 cat than 2 when the baby comes along (although I'm all too aware that he will feel his nose has been put out of joint once the baby comes along! )

We tried the feliway diffuser when our other cat first left but that ran out several weeks ago and I'm not sure how beneficial it was to him.

I do agree with you on the craving attention theory, maybe we should seriously think of getting him another pal, although I'm not sure I could cope with a kitten at the moment!