Ok, I believe it is sorted.
The problem was a combination of things.
1. The hanger was indeed bent, a little bit, in two axis, vertical and horizontal, not a lot, but a bit.
2. The rear mech cage tension spring had slipped out of the retaining hole in the cage, forcing the cage to hang at a slight angle, again not a lot.
3. One stiff link in the chain, the main culprit I think.
Seems ok now.
Thanks for the advice.
Watch out for stiff links!