There are many jaw-dropping moments in Melvyn Bragg: Wigton to Westminster (BBC2, today), Olivia Lichtenstein’s affectionate account of the life of the great panjandrum of arts broadcasting. But the best, for me, comes when young Melvyn, not long out of Oxford, makes his first television film.It is about the playwright David Mercer. Melvyn employed a young man with an impeccable BBC RP (received pronunciation) accent to do the voice-over: himself. The Cumbrian vowels, temporarily locked away, would come back as the Bragg brand was built. Meanwhile, Joan Bakewell, from a simi­lar background, taught herself to speak posh and stayed that way. It is different for girls.I mention this only because Lichtenstein’s film is obsessed with social class. We hear all about Melvyn&rsquo