Niggly niggly derailleur not quite right annoyance

[Fnaar]

I shall investigate further when I can get it to the shop, but may have to just ride it in the meantime. Thanks for all your replies folks, I really am very grateful for all the advice I get/have got on here.

 

[Fnaar]

Reporting back on this (I forgot, for a bit)
Turns out the hanger was actually broken... just held in place by the derailleur... LBS took derailleur off, and the hanger just fell to the floor