Thanks for that Dave, that does sort of confirm the trace I'm seeing and if that Cam sprocket is at TDC then it would appear that the two signals would be out of phase with each other as the trigger points are just before TDC on the cam wheel. I must admit, I can't work out the trace from the crank sensor but I've inspected that trigger plate on the back of the crank pulley and can see no fault with it.

The mystery deepens though as I've now found out that the garage had fitted a replacement engine as suggested by Subaru, but it turned out to be a 1600 engine, not a 2 litre. Apparently, it ran the same but the garage put it down to being the wrong engine. I can't imagine that a 1600 engine would be very happy running on a 2 litre management system so this could be a red herring.