Fixed!! But expensive.
Ok, I thought I should post this as a conclusion to my issue, as so many people seem to have the P0014 / P0015 fault codes without a fix.
Having been through the whole vanos system component by component I came to the conclusion that the camshaft bearing nearest to the exhaust vanos oilway had worn, causing oil to spill out rather than drive the exhaust vanos. By turning the engine over, oil could be seen spilling out of the bearing next to the vanos feed at a much greater rate than the other bearings. Plastigage showed a clearance of 4 thou plus, which is too much. Using plastigage on a good head the clearance is 2.5 thou, and across the whole bearing surface.
So I too the plunge and bought a recon head. Bingo! problem solved.
There are lots of system tests that can be done to pin this issue down, but at the end of the day even the most sophisticated computer readers wont say the head needs replacement.
If you have the Vanos fault codes and the diagnostic equipment doesn't definitively pin down to the problem, it is possible to fault test the system components, rather than replacing components until the problem is fixed!
The vanos sprocket can be dismantled and inspected. The vanos solenoid can be bench tested. The camshaft sensors can be scoped. The ECU output to vanos solenoid can also be scoped; but if Vanos sprockets aren't moving the reading will be the same as the reading with ignition on, engine off. It is also possible to check oil pressure by making a simple adaptor.