My dog is about fourteen months old, all his puppy teeth seem to have fallen out but his bottom canine seem to have the old puppy tooth stuck there, so he has two  on the one side.

Food tends to get caught between the two teeth and smells really bad so I am forever removing the food build up.

Will this tooth just fall out eventually or will I need to take him down the vets to have it pulled out, bit worried about having to go to this extent.

I would have it extracted. Would have thought if it was going to fall out on its own it would have done so by now. Retained deciduous teeth can cause the permenant teeth to grow crookedly leading to a faulty bite.

Definitely have the vet remove it, because it won't go on it's own now and will only cause cause trouble.
:)