David, I think Ralph Wightman was born in Piddletrenthide in Dorset, where he got his rich country accent. You may be right about his not being on Gardeners' Question Time, but I seem to have a rusty memory of him saying, "The answer lies in the soil" on the radio many years ago. I also remember Kenneth Williams of course, as 'Arthur Fallowfield', but I reckon that was a bit later.
Imagine if somebody asks you where you come from and you reply 'Piddle trenthide'. They'd think you were having them on!