Oh yes, that "duty of care" thing.
This has got to be the best gravy train for lawyers in all of this century so far.
It's nearly all bollox, too. Next time it is mentioned, ask for any legal precedents. There aren't any. It is a product of this: you describe a situation to a lawyer and ask him "is there any liability here"? His rate is £250/hr plus VAT. Is he going to say "of course not" ???
ATC have no conceivable liability to GA traffic, in any situation whatsoever short of vectoring an IFR flight into terrain, or a midair involving a loss of IFR/IFR separation in CAS.