Sitting in room MV2 inside Maida Vale Studios felt like sitting in 1944. I was busy imagining a group of men in tweed suits standing round a hang-down microphone with drooping scripts in their hands, the air thick with twirls of harsh cigarette smoke, recording some spirit-lifting Third Programme radio show for all the folks at home sat round the wireless. The Goons. Sing Something Simple. Workers’ Playtime maybe, if we were lucky. I could smell a fair old bit of history sitting in room MV2 in Maida Vale Studios.

Luckily enough, I was there to watch Billy Bragg record a Radio 4 Mastertapes retrospective on his “difficult third album”, Talking with the Taxman About Poetry.

For a growing list of never really good enough reasons, I’d never seen Billy perform live before – even though his music soundtracked my teenage years as much, if not more, than Bob Dylan or The Smiths. I’d scribble down lyrics like “How can you lie there and think of England/When you don’t even know who’s in the team?” in school textbooks, taking them in like political chow for the adolescent soul.

Maybe it was the noseful of history I was getting or maybe it was the fact Billy Bragg was finally stood four feet away from me singing "Levi Stubbs' Tears" with all the reverb redemption and nervous energy as on the record, but I noticed the way he was singing was different, even if it the story he was telling was the same. Subtle little differences that let you know this is a live performance.

Lester Bangs had a similar experience to me. I know, because he spent a whole essay trying to work out Van Morrison’s performance style on Astral Weeks. For Bangs, Astral Weeks was a life-affirming record. Looking back on it a decade later, Bangs said how the album came out at a time “when the self-destructive undertow that always accompanied the great Sixties party had an awful lot of ankles firmly in its maw.”

Today Astral Weeks sounds like a million miles from Kent State, hard drugs’ osmosis into the counter-culture and the great Altamont comedown. Morrison might have recorded it in 1968 in New York, but the plush, velveteen jams suggest something other, as if Van had disappeared into some jazzy caravan a million miles inside the Irish hills.

“Van Morrison is interested, obsessed with how much musical or verbal information he can compress into a small space,” Bangs wrote in 1979. “And, almost, conversely, how far he can spread one note, word, sound, or picture.”

Medicated renditions

Back in Maida Vale and Billy Bragg is busy reprising "Levi Stubbs' Tears" and "The Warmest Room" – every so often lilting away from recorded versions. Pause here, elongated note there. In "Greetings to the New Brunette", that iconic opening drawl “Shir-lee” becomes “–Shir-lee” or “Shir-ur-lee” – a beat added in and played with. For someone who has a knack for writing songs like political slogans, a slight difference looms large in the ear of the listener.

When someone like Frank Sinatra or Elvis does the same thing live, there’s something bored and over-familiar about it. Gravitating from Las Vegas restaurant to Las Vegas green room, singing the hits for wealthy punters year on year. Medicated renditions that mean nothing to the performer anymore. They become just a song. A self-aware, half-ironic and cutely packaged return on the astronomic ticket price at the door. Surely the Bard of Barking couldn’t fall into the same trap?

Performers like Van Morrison and Billy Bragg tend to live out their songs on-stage. Van can close his eyes and riff off the same phrase for five minutes when he closes his eyes the song is like a road he’s been down a hundred times before, where some new observation always jumps out at him. A word, memory, image. “Caught one more time, up on Cypress Avenue.”

Billy’s word exist in the more tangible world of the political pamphlet, where phrases can change shape so long as they have meaning. And sometimes that meaning changes too. It’s one of the upshots of living in the here and now, as he said himself.

Another leap forwards

When Billy made his first flashy “network television show debut” on the Letterman Show in 1988, he was singing about Che Guevara and drawing the dole. But this "Waiting for the Great Leap Forwards", a delightful two-fingered salute to the Reaganite glitz and New York finger-clicking going on around it, was a very different song to the original.

By living in the here and now, or 1988, Bragg was taking a protest song from a particular moment and placed it into a new one, sometimes even the moment he’s stood right in: “It’s a mighty long way down rock’n’roll, from East Berlin to the Letterman Show.”

Another great leap forwards to a 2007 Henry Rollins Show performance and the song is barely recognisable, with Bragg bending lines into shape once again: “They shake their fists in anger, and respectfully suggest/We take the money from our missiles and spend them on our hospitals instead.”

When Billy is singing the hits, he’s not bored. He’s up for it. Like Van, Billy Bragg has always been interested in the “verbal information” on a line, not so much how it fits but what he fits into it. A poetics of progress, the sort that Dylan claims – gotta keep movin’ to keep from dyin’ – but which rarely extends beyond a new keyboard arrangement with a lapsteel solo wedged in.

Waiting ten years to hear a variant of a favourite song might be annoying for some people, but it’s a sign of Billy Bragg’s commitment to progress in art as well as politics. And that’s something to be grateful for.

The first part of Billy Bragg’s Mastertapes airs on Radio 4 at 3.30pm today.