Disconnecting the MAF (having drilled the head torx screw that was rusty to remove and work out how to disconnect the wiring clip which was not easy!) allowed the engine to rev and all seems good (tick over still marginally lumpy). Cleaning the MAF with MAF spray didnt help so a new one is on the cards.
I think I'll still do the AOS which reading 101 Projects suggests that could be the cause of failure. The car is triptronic and access seem terrible so I'll set aside some time for that. Incidentally the corrugated pipe coming to the AOS was split and bodged with duct tape which may have been the squeal originally heard?
Anyway thanks to Oggie and Nieuwhzn for replying - I think I'll put the fuel filter on the list..