Going behind the scenes of Nick Clegg's LBC phone-in show The Global offices, which also house the more youth-orientated likes of Capital and XFM, are full of bright lights, loud music and funky soft furnishings, ensuring that Nick Clegg, as he strides down the corridors in a stuffy suit, looks like a deeply uncool member of the legal department nipping off for a loo break. But once he's shut in the studio for his weekly Call Clegg phone-in, with his small entourage of interchangeable minions waiting outside the door like particularly weedy bouncers, he seems more at home, loudly greeting Ferrari like an old friend, even remembering to ask him about his bad back. It's funny that Clegg started last week's show, which I sat in on, with a self-indulgent happy birthday message for his sister because it's really his employers, LBC, who should be receiving a cake and a card. Today it's 40 years since the London-focused news and talk station launched; and the jewel in their crown that is the Call Clegg show, with its regular, direct access to one of the most powerful people in the land, is token of quite how big this supposedly local station now is. No national station boasts an equivalent. It now competes with the stations that it has influenced, from BBC Radio Five Live to the digital talk radio stations. Six years ago LBC - which stood for London Broadcasting Company - was rebranded as London's Biggest Conversation and, with both Clegg and Boris Johnson taking on regular phone-in slots in recent months, it has some right to that claim. For nine months now, Clegg has been turning up to face the people of London (and indeed the rest of the country - thanks to the powers of digital, one of last week's callers was from Fife). Ferrari says that the topics Clegg tackles each week are spontaneous and for the most part, this seems to be true - although every caller who's made it on air has been through a strict filtering system that removes the blatherers, the swearers and the downright barmy from the 10,000 callers a week. However, I did spy a note on a producer's screen reading "Things he's keen to talk about: Cameron speech, Osborne speech" and I also overheard Clegg saying to Ferrari, just before going live, "If you've got an anarchist, that would be good." Anarchists on demand - sort of defeats the object, doesn't it? Clegg used last week's show to voice his views on the ongoing drama between Ed Miliband and the Daily Mail, offering his thoughts seemingly casually, but undoubtedly aware that everything that came out of his mouth was a sound bite. Ferrari, whose political allegiances lie with the Conservatives, is, of course, delighted to have scored the coup of a weekly slot with the DPM, but admits he'd love it if Clegg made a huge gaffe live on air. "So far we've only locked horns once, over whether he was sending his kids to private school," he says, clearly hoping, like the good tabloid man he is, that one day Clegg will choose his show to say something rather more explosive. It says much for the 40-year-old talk radio pioneer LBC that it has managed to put such a potentially incendiary combination together on air.