Quick update,
I took my car to a friend who is a refrigeration mechanic. He connected up the gauges and it was showing around 60psi on the low side.
(Engine running = Everything in spec & no gas needed according to the VW manual)
After starting the car and rechecking the compressor clutch, electrics etc he said it's most likely a failed compressor because as you rev the car it's not "pulling down".
I'll take off the serpentine belt and see how easy it is to spin by hand but looking at this logically it can't be anything else.
Was is interesting is that it failed but didn't leak any gas!
So I'm now looking for a new compressor
