OK, problem resolved. It looks as though the situation is as follows:
According to the DVLA Medical Rules for Drivers, if you hold a car or motorcycle driving licence you will not need to tell DVLA about deafness or hearing loss.
If you hold a bus, coach or lorry driving licence, you will need to tell DVLA about your condition, if you are profoundly deaf. They will want to satisfy themselves that a driver then has a proven ability to communicate in the event of an emergency by speech or by using a device e.g. a MINICOM. If unable to do so the licence is likely to be refused or revoked.
Source: At a glance Guide to the current Medical Standards of Fitness to Drive, issued by Drivers Medical Group, DVLA, Swansea.
I have contacted the DVLA Helpline, and they confirmed that there is no question related to hearing loss or deafness on form D46 or D46P – renewal of licence at 70. So the same rules apply after 70.
If you know otherwise, please let me know.