I have an 11 week old pup who has a slightly undershot jaw (his bottom teeth are slightly in front of his upper teeth) - is there any possibility this may correct itself (though I know its usually the lower jaw that grows at a slower rate therefore it's likely to get worse) - we bought him to show :( He had a correct bite at 8 weeks of age but it is slowly getting worse.

It depends on the breed and which bite it is supposed to have.  If a scissor bite is required then at this age you generally want a small gap with the teeth being slightly overshot (in Dobermanns anyway).

It *may* change when the adult teeth come though as mouths go though a lot of changes during this time.  Stop looking for a few months and try again when he is about 20 weeks

I doubt it will correct itself, in fact I am pretty sure it won't.  The bottom jaw is the jaw that grows for the longest time.  As Keriok says a small gap between upper and lower is ok as the bottom jaw will meet the top one once the adult teeth are in.  Undershot jaws are very common in short muzzled breeds such as Bull Terriers.
Dawn.

i have had puppies which have had undershot jaws which corrected to scissor  but this hasnt happened often.
i wouldnt class bullterreir as really short muzzles(maybe cos i have breeds which have real short muzzles in comparisons)

If the teeth only are affected, then give plenty of big, raw meaty bones to chew on (plenty to work the front teeth on) and the teeth should come through correct with correct use.  If the bone of the bottom jaw is longer then I don't think there's any way you can influence it, all you can do is keep your fingers crossed and wait. 

no offence but i cant see how chewing big raw meaty bones will help.
a certain occlussal classification wether bone relationship or by teeth is more or less fixed unless with surgery or orthodontic measures.

LOL,  I have seen it done :D  it works very well, but only when the teeth only are the problem, if the jaw bone is affected this is not going to work.  As the baby teeth fall out the act of tearing at the gristly bits on the bone with the growing front teeth helps them to attain the correct position.