Well, it turns out that the oil pump had gone, and apparently the original garage had subcontracted the work to a guy who had worked at vauxhall dealership for 15 years and he had told the garage that he thought that the oil pump wasn't great and could do with replacing but they didn't tell us, anyway we're now dealing with this guy direct and he knows his stuff so am feeling happier, he's now putting us another engine in which he knows is a good one, it's costing us but what can you do, at least I get my beloved car back, thanks for your help guys.