My dog is 3 months old and she has had all vaccinations. She has had worms and we thought they were clear but now she has got a small amount of blood in her poo and is this linked to worms? If not what is it serious? However she isn't ill what is this?

Matthew, is it possible that she got a hold of something, chewed and swallowed it? How long has it been since she was dewormed? Whatever the cause (and there can many reasons), blood in stool is not a good sign. I suggest you get a sample and bring it into the vets tomorrow to have it analyzed. If nothing turns up, it would be wise to bring her in for a physical health check.

There are several things that cause blood in the stool, none of which go way. See the vet as Ruby said.