Oh Bu99er! Have the oil and water mixed?
You might get luck and it be a stuck valve/jumped timing belt.
If you can get it to Bristol, I highly recommend Duncan at Alfanet Services.
Oh, ok your sorted, just one of those things I suppose. Whats the mileage on the engine?
Andy, as one valve has let go, don't you think you should replace the rest of them?
While it's apart.....what about turning it into a 3.7??