Thanks all. I don't think I could actually put them down- and if I did, I know would feel terrible, so in reality its not really an option- mainly frustration speaking. (Bathsheba, you will be appaled to hear that when my big cat was young and I got him from the shelter, his behaviour was so bad that I was advised by a vet to put him down because he "wouldn't change". I couldn't do that and lots of love later he is a much happier cat. So I think if I could go through that with him, I couldn't get rid of him now!)

But I know something does need to change.

We have been thinking for a while about re-housing the little cat and keeping the big one. Do you think this would make it easier or harder on the big one? They don't get along great, but at least they are kind of company for one another.