That is wonderfully funny!
I am sure that people buy a brand and nobody really cares on the whole to this day how it is done.

And don't you just love my terribly posh ex public school accent.

Strange how we lose these things.

Yet Michael Frayn described my voice as "demotic" (of the people).

I thought it was dreadfully plummy.

My accent tends to go with how people are speaking at the time. I came back from Ireland speaking pure Dublin. It is very difficult to shut ones ears out and speak like you want to be heard. When I am with my Mum and family, we are all probably illegible to most, as the accent becomes too strong for most to understand.
In Glasgow, recently, they thought I was from Australia.
Accents are wierd things. In France, even the dogs in the mornings, seem to say "Le Woof!"
An RSPB study, even checked out regional accents on birds, claiming local dialect on their calls. This was not incorrect at all, in the UK, the Wood Pigeons blatantly say " I Want some bread now Baby!x 2".
On the continent they seem to say, "Ou est le pain? (pause), now baby!" ( x 1, then go down and get some for themselves.)
The amount of the little grey , fat things lining up for food in the morning at the bakers can be amazing as they search for crumbs. (Their cards are normally not accepted,... bad credit profile, pigeons....)

Seriously though, a good TV voice there man. Not an easy thing.