Do Radiohead songs ever baffle you?

Ed: No. Yes. Sometimes -  but then I ask Thom, which is cheating. The lyrics rarely confuse me. On In Rainbows I liked the fact that he was writing about universal human emotions again, which he hadn't done for a while.

Colin: Frequently, at the musical level. You mean lyrics? Um... there's a song called Weird Fishes which evokes meaning rather than states it... the chord changes bear you aloft and sweep you back down and that's a sort of meaning. If all you're looking for in music is a way of talking about it, it's pretty poor, isn't it?

Late that afternoon, Radiohead are in the concrete bowels of BBC Television Centre, preparing to appear on Friday Night With Jonathan Ross. Outside in the central atrium, Radiohead's drummer Phil Selway and I sit in a peculiar wooden alcove and drink the famous BBC tea. It's not as bad as 50 years of comedians would have you believe.

If there's a perfect contrast to the popular idea of the rock drummer then Phil is it. He is delightfully wry and funny, even - and I'm sure he wouldn't mind the idea - ever so slightly camp in his mannerisms. Now a father of three, he coped with Radiohead's extended lay-off by concentrating on being a full-time dad. "When you tell people, 'I'm taking some time out from work, I'm an at-home dad,' they immediately glaze over. Then you mention being a musician and the facial expression says, 'Hmm... unemployed.'"

What's harder, dealing with a band or dealing with kids? "One's good training for the other. I'm not saying which one's which."

I ask him about Thom's comment about his confidence - it struck me as odd that members of one of the world's biggest bands could doubt their own abilities. Radiohead are not all lack of self-esteem, Phil says. But maybe collective dependency is a better word than confidence.

"We feel a big responsibility towards one another. I don't know if it's because we started in a school band, with all the bravado that goes with it. Every school band thinks it's the best band in the world, and then you get into the proper music industry and you feel a bit fraudulent. We're the same five people so we have the shared history of feeling like that." He misses the mad confidence of youth. The first gig he ever played, he'd never sat behind a drum kit before but it sounded alright. "I'd never ever do something like that now, and yet we've sold X million records, we're quite well thought of. You'd think that's do something for your confidence but it doesn't. That teenage exuberance and unquestioning self-belief, you think, 'Where did it go? I want it back.'"

We go upstairs to the canteen where I join Jonny Greenwood, Radiohead's youngest member and the broadest interpreter of the word "guitarist" in music today, for a plate of exemplary BBC roast potatoes. Jonny's excited to be at the BBC at all. "Last time I came here, I saw Michael Fish," he declares. As an aficionado of British comedy - from Round The Horne and Julian and Sandy to The Mighty Boosh - he's practically breathing in the history. One of his proudest moments is hearing Jeremy Hardy singing the words to Creep to the tune of Grandma We Love You on I'm Sorry I Haven't A Clue.

Apart from Thom Yorke, Jonny is the member of Radiohead with the busiest extra-curricular life. His soundtrack for the Thomas Anderson movie There Will Be Blood was nominated for a BAFTA this year, although Jonny says soundtracks are "a bit of a con. You get access to a roomful of incredible musicians who can make whatever you write sound brilliant. Your slightly shit three-note chord will sound absolutely incredible in their hands. I feel like I'm getting away with something."

Being at the BBC reminds Jonny of Nigel Godrich, and how they missed him when he wasn't around. "There's something institutional about Nigel," he says. "Something quite BBC-ish." Godrich once told Jonny that he at his happiest when simply plugging things into a rack of equipment. He made a mixing desk out of a plank of wood and some yoghurt pots when he was seven years old. "It's borderline some kind of syndrome, isn't it?" says Greenwood. "He'd have been very happy in this building 40 years ago, walking round in a white coat. Working with Spike Stent felt a bit too much like there was an adult present. With Nigel we can reminisce about old ZX Spectrum games. He's our generation. It feels more like we're in it together."

Stage managers appear and wave photocopied schedules -  the band will be on in a bit. Over the past few weeks of listening to Radiohead discussing their working lives and private worlds, I've heard reflected back at me the same concerns that make most of us in the middle classes tick. Perhaps, boiled down, it's simply a desire to do your best and not make a song and dance about it. Are Radiohead really just the most self-effacing band in the world?

"No," says Jonny, "because when we've done something good we know it. We've got that middle-class work ethic that stops you being overtly impressed with yourself, but inside we know that something like Pyramid Song is a great recording and we're really proud." It helps, he thinks, that the members of the band don't feel individually responsible for its work. "It's as if Radiohead is an institution, or a company you work for, and people really like their product. We're just working for it."

An hour or so later Radiohead round out a Ross show that features David Tennant, Catherine Tate, John Hurt and reptile-wrangler Nigel Marven. They play Nude and 15 Step, the spectral ballad and techno-jazz squaredance puncturing the programme's air of enforced jollity and making you wonder about, you know... stuff. Perhaps this is what we want of rock music in the 21st century. Something doesn't add up, something that's impossible to nail down, something that slips through your fingers like the weird fishes of Radiohead's dreams.