Was talking to mechanic at a vauxhall dealer today and happened to get onto the subject of the timing chain issues and I mentioned about the oil jet side of things and he did say that a revised jet was fitted with larger nozzle which I knew about , but however what he did say was that a lot of the problem was not so much the Jet but the oil filters breaking up as they of paper type and this was causing restriction of oil flow, which kind of makes sense, so probably the moral of the story is to keep a check on these filters!!
Cheers Pete