StephanZ - that is an interesting point but I know how old he is, this is becasue as I mentioned the owner was my boyf's sister who only lives a few minutes walk away from my house so we see each other often out and about. She told me about the kittens on July 31st and told me they were ten days old at that point.
I have no doubt she might have forgotten how old they are now but I have been keeping track! But you might be right that she said ten days when it was actually only a few days or something - maybe he is a bit younger than we thought.
Either way he is doing much better and, asides from another quick call to the vet to ask about supplements we are very pleased with how he is doing so far, he is getting very inquisitive and we are having some success with drinking from a bowl and mushed up wet food now. Can't wait til he is feeding himself properly though as I am KNACKERED from getting up and down during the night to offer him food as he still won't eat unprompted, he will look for food but will literally walk right through a bowl of milk and keep looking unless I am holding it up to him. I am still giving him nightly baths which has just as much to do with getting the milk from his impromptu swimming sessions off of him as it does to do with how much he likes it!
Thank you all very much for your help and advice, I really couldn't have managed without it.