Thank you your replies, inlcuding ATC watcher. Remember this thread was triggered by an ACAS 11 memo from Eurocontrol and it seems to be proposing, even stating, that this will become the procedure in PANs OPS due to be published soon.
They lumped all a/c degraded performance scenarios together, only giving engine failure operations and emergency descent as 2 examples of applicable TA only operations. Thus, if it is adopted, then company SOP's will lag behind, naturally.
Regarding the turn off airways, we had been briefed that NATS expected an emergency descent straight ahead and let TCAS & ATC sort out the problem. I can just imagine the bells ringing, when 5 a/c all south bound from Scotland into the various London airports, all on // radar headings, and then 1 one the maggot on the screen suddenly storms off stage-right like a bowling ball on acid.
Anyway, we shall have to wait and see the outcome of Eurocontrol proposals.
We had also been advised that in less crowded free-fly European airspace a slight turn off the airway should be considerd. Either way the old 90 degrees peel off seems to have been binned.