I must admit I was surprised at the advice too, hence posting on here!
He's showing no other signs and the blood is drying up now. I've checked his teeth, eyes, what I can feel for bone damage, and he genuinely seems normal. He doesn't get upset with me prodding at him, unless i try and wipe the blood - then he sneezes over me.
It wasn't my usual vet - they have an answerphone message for out of hours that diverts to a 24hr line depending on the area you select. This was some place in East Molesey. I'm not even sure where the nearest 24hr drop-in is from here. I'm keeping a close eye on him atm and will ring my actual vet tomorrow whatever happens.
This kitten must have used up at least 2 lives already!