Hmm - let's turn this round.....
I wonder what would happen on a validation board if the candidate gave radar derived info to aircraft on a Basic Service, was told he had failed because the Examiner thought he had broken the "rules" & he said "I was excercising my duty of care " ? I wonder how LCE's are going to handle this.......
He would have failed because he was simply not adhering to the service description - he wasn't 'exercising his duty of care'.
'Duty of Care' is not something you do in addition - it's part of the law of negligence so it only comes into question when things go wrong. I don't believe you can enhance duty of care by doing more than you are asked to do.
In fact if you start giving radar based traffic under a BS, then if the one time you don't give it, someone smacks someone else - would you be negligent for not providing the same service as you did before?
The answer is simple - provide the service the way you are supposed to. If it all looks sh!t and you simply can't watch the horror unfold, then do something. But for goodness sake don't just start doing things because you think you are helping or 'covering your duty of care'. You'll only end up in the crap whe it all goes wrong