Meeting the members of Radiohead over the next couple of weeks I'll sense a lot of relief, satisfaction and even quiet amazement that the In Rainbows project – protracted recording, abrupt online release, surprise shows –  has turned out so well. Colin thinks that the past few months have literally rekindled his passion for music; not an insignificant thing given that during the recording he temporarily lost part of his hearing from using the wrong headphones. "It came back, mostly," he says. "It doesn't feel like I'm talking to people underwater any more. For a few months afterwards I'd be watching the telly and suddenly hear these high-pitched whistling noises as more and more high frequencies came back. If you're worrying about how you hear it instead of what you're hearing, it completely gets in the way of making the music. It was a fucking nightmare, actually."

As, by the sound of it, was the recording of In Rainbows. After taking 18 months off work after the end of the Hail To The Thief tour, they endured a false start in making the new record with producer Mark 'Spike" Stent, who'd worked with artists as varied and non-Radioheadlike as Madonna, Keane and No Doubt (each member of Radiohead will take pains to lavish praise on Stent but accept that the combination of talents wasn't right). The process became enervating; they recorded some of the songs four or five times and felt no nearer to a workable record. Then Nigel Godrich, who had grown with Radiohead from engineer on The Bends to co-developer of their sonic imprimatur on OK Computer, became available again. "We realised afterwards that we were always waiting for Nigel," says Colin – "making plans for making plans with Nigel." The recording began to move forward. But do they always have to make such heavy weather of it?

"Yes, it's all going wrong, we're doomed... We do make it hard for ourselves, probably unnecessarily so. We still get the red-light fear when someone presses 'record' – the fear of finally committing something and having to stand by it. We definitely get that with live TV too. You become so frightened of making a mistake that you make the mistake anyway – it's when you manage to not care too much that you can play really well. It's a middle-class thing. We were brought up to care too much, or worry too much, or care about the wrong things."

One thing Godrich did to unblock the band's thinking was to employ deliberately primitive recording techniques. This meant that, secretly, In Rainbows would be strongly influenced by the Jungle Brothers, A Tribe Called Quest and early '90s hip hop. Godrich wanted to transfer or "bounce" all the rhythm tracks down to a single track of tape, where it would be fixed and immutable, rather than keeping them on multi-track where the band would be tempted to fiddle with them. "The idea was to make us commit to something," Colin says. "You know, ‘You've done it now and you can't change it.' It was as if we were sampling ourselves. And when you mash sounds together like that they cross-pollinate, they marinade, they interact with each other... they have little sonic babies."

The result, after a further year of work, was probably the most beautiful and even joyful record that Radiohead have made. If The Bends was about them discovering their talent, and OK Computer was about deciding what to do with it – and if Kid A and Amnesiac were about testing the limits of what a rock audience would accept – then In Rainbows put everything that Radiohead and Godrich had learned into the service of the best of human emotions. Yorke's lyrics may have mined insecurity, fear and personal disconnection but the music made a more sustaining connection of its own, from 15 Step's infectious drum'n'bass hopscotch to Body-snatchers' grunge-with-a-PhD rush to Videotape's hypnotic, piano-led vision of the afterlife. It's the Radiohead record that most bears incessant re-playing and its suggestion is that –  though the infrastructure might collapse, though you might be eaten by the worms and the weird fishes, though you might be trapped in your body and you can't get out – what really energises this world is love.

In Rainbows also marked a step away from the clumsy politicking of Hail To The Thief, which from its title down tried to get a handle on the neocon/Iraq era but ended up feeling like incoherent rejectionist slogans. This was partly because Yorke's lyrics were typically abstract and partly because the febrile run-up to the Iraq War seemed to dissolve rational argument: you were simply either For or Against.

I ask Colin how he feels about Radiohead's political dimensions, which are usually articulated separately from the music, by their affiliation with campaigns or Thom's interviews. Everyone in the band backs the climate change stuff, he says, and he explains in detail the lengths they've gone to to reduce the carbon footprint of this year's tour. An environmental audit by Oxford-based company Best Foot Forward indicated that buying two sets of live equipment and booking a conventional tour meant more audiences would simply drive, or fly, to the big gigs. So they bought the kit and the revolutionary low-emission LED light show. "It's very exciting," Colin says, "but without the big Rock Lights it's going to be fucking freezing onstage." Then he tells me how interested he's become in the books of Nick Cohen, Oliver Kamm and Andrew Anthony, the blogger Norman Geras and the blog/website Harry's Place, all of which look at how the liberal left has lost its way and which have been vilified by the Stop The War wing of the left as rebranded neoconservatives. Colin considers himself mildly addicted to the new world of information. "I'm the old curmudgeon in front of my computer," Colin says. "It's the new version of shouting at News At Ten."

Colin loves soul music, Spank Rock and old techno; has just discovered Black Sabbath ("brilliant!"); has developed a interest in Fleetwood Mac ("the band are a bit worried about it"); and has a debilitating tendency to reach for the tambourine whenever he's not doing anything on a song ("the others have started hiding it from me, the bastards"). He also loves art photography: the work of Gary Winogrand, Joel Meyerowitz, street photographers like Walker Evans or Farm Services. As he drives me to Oxford train station he tells me how much he loves the new Underworld record Oblivion With Bells. Radiohead went to see them when they were making Kid A/Amnesiac in the punk-hippy enclave of Kristiana, Copenhagen, during a break from recording Pyramid Song and came back full of enthusiasm. It's funny how their own records are often punctuated by seeing other bands, he says. "Making The Bends in spring 1994, we were having a crap day in the studio so John Leckie said, 'Come on, let's go and see Jeff Buckley at the Garage.' Then we went back to the studio and Thom recorded Fake Plastic Trees straight away. It was genuinely, properly inspiring."

He pauses and drums his fingers on the wheel. "We need to get out more."

Read Part Three.