parkus:
Usually people of that level of erm… not being able to do everyday things, have someone pre-authorised to take care of bills and legal correspondence.
That would be myself (as appointee) for certain things like dealings with the DWP etc.
I organised him a postal vote for last year’s Brexit election and he did manage to sign the form but his vote was not allowed because his signature was not the same as the sample one they got some time back.
Doubtless it will be similar with the DVLA wanting a signature (dad can’t even hold a fork now)
so we will just ignore it and it will go away.