Thanks again for your replies,
The harness does sound like a good tool, the problem is that I cannot physically hold him back when on the lead or halti and when he is "leaping" he pulls against it. So I guess so long as he cant pull or "brace himself" against harness, then it could well work.
Basically what I do when he pulls I use the choker technique as mentioned above or try to make him sit, I never just let him go or go with him. If I really can't get him to stop or get under control I will try and get him to lie down or wrap the lead around the nearest solid object.
I have tried to get him to walk backwards, sometimes I can other times I cant physically do it, just depends on what the situation is and how strong he's reacting.
For example when leaping at other dogs yesterday he is standing on his back legs bouncing up and down and all I could do is grab him by the collar and wait until the other dogs is passed.