There should be no issue to not consume nuts if it means the health of a fellow passenger.
Does BA have a specific policy and procedure regarding these announcements? Do passengers with allergies have to provide advance notice? Does the cabin crew check to see if they are carrying epi-pens?
I know on Air Canada they will implement a "nut buffer zone" if notified in advance and the FAs are very strict about seeing epi-pens and requiring they be stored close at hand and not in the overhead. Does BA do the same?