Chewing on leash

I've been trying to train my pup to walk on a leash but every time I pick it up he instantly bites into it and won't let go, so if I did lead him anywhere it'd be by his mouth. I've been getting him used to having it attached; if it's trailing behind him he doesn't have a problem at all, it's only when I pick it up. I don't put any pressure on the leash, it's just the fact that I'm holding it that makes Splinter decide that he'd like to hold onto it.

I've tried putting that anti-bite spray stuff on it, which does keep him away from other things, but he seems to be able to bear the taste when it comes to the leash. I'm not sure how to go about it to make him stop, I don't want to try walking him anywhere if I have to lead him by the mouth.

There was one time he was alright on the leash - we were driving to Adelaide (a 4 hour drive) and stopped a few times on the way at rest stops so he could do his business and have a bit of a stretch, and he walked on his leash perfectly for me (this was after I had tried him at home, with the same biting result, and he keeps biting still). The noise of passing traffic on the highway calmed him down to make him the perfect little walking angel. But in the comfort of our backyard he seems greatly opposed to the leash. Any ideas on how to stop him biting it?

I have to say I am ruthless about this with my own puppies. Leash grabbing has very unpleasant consequences around here. If any puppy grabs the leash here it is removed very abruptly.

Other things to try:

Offer the puppy tasty treats to get it to spit out the lead.
give the puppy something else to carry. A toy. A dowel. A stick. A dumb bell.
Turn your back and stand still each time the puppy grabs the lead.
Teach the puppy to play tug, and how to release. Then if the pup grabs the lead, you can play a few minutes of tug, and then ask him to release.

I agree with what Red suggests. If your yard is fenced you can try walking around, talking to the pup in a high voice, having fun and as soon as he bites the leash drop it, turn around and walk away. Also you can redirect to something else like a toy right when you see him show interest in the leash.