Centrica would have done a seabed survey. Its a long shot, but given the family connection they might see positive PR in advising if there are any likely targets, and where they might be. Or they might decline...worth a phone call perhaps?
If Centrica did find an aircraft crash site and wanted to disturb it, a permit is required. If there is a risk of UXO, or is known to involve casualties, a permit would probably be refused - guidance notes
here.
If a permit has been issued, Joint Casualty & Compassion Centre would be able to advise. Again, worth a phone call. Their contact details are in the link above.