Hi Kev
All sorted finally, but not a cheap fix and ended up to be the timing chain, which had stretched due to low oil at some point. Jaguars does not come with an oil light indicator so need to monitor this regularly. If you find you are losing oil it is probably your oil plug on the timing cover, which the seal is broken. The plugs are cheap and need to get looked at when replacing the chain. Sorry I have no good news, but I found out the hard way and spent £1000s to get to the actual problem.
hope this helped.
Ian