Hello thanks for replying, sorry not sure of his exact weights (not helpful) but he was over 4kg - I know that from his advocate dose. The vet said it may just be stress related and I am taking him back beginning of jan for another weight check. I think if he has lost more weight then will ask for blood tests etc.
Just seems odd that he has consistently been loosing weight but seems otherwise fine
If you've actually noticed that he's skinny (and you tend not to clock things so quickly when you live with an animal day to day) then I think I'd be tempted to vet him sooner rather than later. It's a fairly long time to January in a cat's life and things tend to go to pieces over the Xmas season in any case - with knock-ons due to backlogs etc, sometimes.