if fresh (bright red) blood it may be a small rupture in a blood vessel which should clear up on its own. If dull red it may be a sign of something more serious that requires veterinary attention. Either way take pussy to the vet if it doesn't clear up on its own pretty soon. ps I'm a responsible pet owner not a qualified vet.
With the greatest of respect, I am always surprised by people who take the route of posting questions of what appear to be fairly serious conditions on here first rather than getting their animal straight to the vet. If for any reason you are unable to do so, my advice would be to phone your vet and they should be able to advise you on how quickly you should be taking your cat in.
I very much hope it is not too serious, best of luck, Sue.
with the greatest respect sue11 i posted this question at 5.54 this morning when my vet wasn't open just to get some ideas before i went to see him which i will be later today