David Beckham set to star in new Gavin and Stacey

David Beckham is being lined up to star alongside funnyman James Corden in a one-off special of Gavin and Stacey.

This could possibly be the most deranged variety show you'll ever see, the only place on earth where you can watch Christopher Biggins pretending to be Boris Johnson, and Jerry Hall impersonating Katie Price. If that doesn't draw you in, how about Joe Pasquale as Lady Ga-Ga? Or Ulrika Jonsson as David Beckham? No? Surely Vanessa Feltz masquerading as James May is irresistible. As is Eamonn Holmes as Elvis Presley. And David Gest as Elton John. Les Dennis as Gary Barlow... The list goes on, and just gets odder. The All Star Impressions Show could be completely awful or it could be enjoyably barmy. It certainly has a very good pedigree, being co-produced by Steve Coogan's and Vic Reeves and Bob Mortimer's production companies. And it has a certain surreal gloss that could be quite winning. Harry Hill will make a guest appearance, though we don't know whether he will reprise the Morrissey impression that won him Celebrity Stars in Their Eyes all those years ago.

Chain Reaction (Radio 4, Tuesdays, 6.30pm) has been the highlight of my late-summer listening. Through it I've come to like Frank Skinner, discovered that Eddie Izzard can still throw aside the ponderous trappings of Hollywood semi-stardom and be himself again and found, in Alastair Campbell, a charm that he managed to hide so successfully during his years as Tony Blair's minister of propaganda. And every week I've told myself that, this time, I'll resist the temptation to write about it here and focus instead on the new.

But then last week Campbell only goes and interviews Alastair McGowan and all best intentions exit stage right. Last Tuesday's Chain Reaction was probably the best of the series so far, as McGowan gave a masterclass in how he does what he does so well. Slipping from one voice to the other, frequently during a single sentence, he analysed how they came to be. The Nerd Voice, for example, which he was already using as a generic, suddenly acquired a real-life person to attach it to: John Major. "The reason why it's the Nerd Voice," he said, "is because it's completely devoid of emotion and heart.

"Technically, it derives from the back of the throat, which is also used by Brian Perkins" - changing gear ever so slightly to become the legendary Radio 4 newsreader - "but Brian has a connection with his chest, so you have this wonderful, resonant open voice, while Major" - shifting the voice a couple of inches upwards - "is stuck in the throat, so he's cut off from feeling.

"Michael Heseltine," he continued, on a roll now, "had a fabulous oratory voice. He had a trapped 'R' and he couldn't speak properly, but when he really got going he was trapped and there was a little bit of shyness there and there really was a great power to it."

And by God he was right. So simple, and yet so intricate. "There are places the voice goes to," he summed up, "and the deeper it goes, the cooler you are."

Prompted by Campbell, McGowan gave us his Tony Blair, which derives much of its authenticity from the former PM's habit of replacing his "I" sounds with "U" sounds - "Uff the Honourable Member thunks..." but confessed himself stymied by the next PM, David Cameron: "Just sound posh and whisper."

But of course, McGowan is best-known, not for his political voices - Rory Bremner has that covered - but everything else. David Beckham, for example, is an unconfident Stuart Pearce, and when McGowan segued from one to the other you saw exactly what he meant. The same voice, but with a different man behind it.

Look, the latest series of Chain Reaction will soon be naught but a beam in the eye of memory (McGowan talks to Simon Callow today; should be interesting), and I'm going to write about something else in a minute, but there was one last McGowan moment to warm our way into winter. "I've recently discovered Neil Oliver, of The One Show," McGowan said, in Scots character, "and one thing I've noticed is that he's really passionate about everything he does, but he really has to keep his passion under control, because if he ever gets carried away with it, he's just going to turn into" - mid-sentence segue - "Billy Connolly!" The mind's ear caught the connection and thought 'I could do that.' As if.