House music: Tony Benn's debut solo album

Political firebrand Tony Benn is about to mount an assault on the pop charts – in the debut solo album of Mull Historical Society's Colin MacIntyre

"It's a battleground, not a museum," says Tony Benn, turning to look back at the Houses of Parliament, the place where he was baptised in 1925. It's the end of an afternoon in which he has shown Colin MacIntyre, the man who for three fine albums was Mull Historical Society, all its secret corners.

MacIntyre's debut under his own name, The Water, is also Benn's debut as a poet, after he was invited to complete the album's closing humanist anthem, "Pay Attention to the Human". But as MacIntyre and I are led through the Commons, the wider question of pop's continuing connection to politics looms large. MacIntyre's father, Kenneth, whose death inspired Mull's first album, Loss (2001), was the BBC's top political reporter in Scotland; The Water was partly sparked by the war in Iraq. Benn, meanwhile, has spoken at Glastonbury, has sold 30,000 copies of Tony Benn's Greatest Hits (1998), an album of speeches remixed by Charles Bailey, and next month will be at Brixton Academy to celebrate 30 years of Rock Against Racism. The pre-Pop Idol world of the early Eighties, when anti-Thatcher demonstrations and independent music were intimately wed, seems close as we talk.

"I do believe that art and politics are very close together," Benn says, as we sit drinking tea on the Commons terrace overlooking the Thames. "Because it is the culture of the working class. And because the imagination and art is international. Popular music isn't really my subject. But I was stirred by Colin's song. The strength and clarity and power of it excited me. And its humanist values speak to people of all religions. Religion can be terribly divisive. What he does with his songs unites the human race."

"I hate seeing musicians get on their soapboxes," MacIntyre says. "I cringe. But if you can subtly represent the idea that music and faith and politics work together in your art – well, what else are you trying to do?"

"I went to his house to meet him," Benn says of their collaboration. "Recording in his basement gave it this otherworldly echo." Benn's poem, presenting a stark "moral choice" to save or end the world, follows MacIntyre's own lyrics alluding to the death of David Kelly, and insisting on humanity in a time of technology and war. It's an internet-era "A Day in the Life", glam and grand.

An hour before this exchange, Benn is inviting MacIntyre into the broom cupboard of the Commons crypt, to see the plaque he has put inside to commemorate Emily Wilding Davison, the suffragette who hid there the night of the 1910 census to declare that Parliament was her place of residence (and who died throwing herself under the King's horse at the 1913 Derby). Benn turns out to have littered the Commons with plaques, always without permission. "I'm too old for that," the 82-year-old claims, but his impish attitude befits a much younger man. When a plaque in honour of the unsung workers who have contributed to Parliament was left to rot, he returned with an apron and mop to scrub it. Every worker here knows him, and is greeted with as much warmth as when he bumps into his son Hilary. Benn's father, like both his grandfathers, was an MP, and, like Benn himself, joined the RAF in the Second World War expressly to fight fascism. "I wouldn't have liked a 67-year-old in my rear gun turret," Benn says.

He brings history alive at every corner we turn in the place that is, in some ways, his home. The grand chapel that Cromwell whitewashed, before the Great Fire uncovered its paintings of saints being broken on the wheel and burned in oil, becomes an early chapter in the so-called "war on terror". In the steel-and-glass of Parliament's newest wing, meanwhile, statues of Thatcher and Churchill loom over cappuccino drinkers. Benn's portrait there sneaks Karl Marx, whose bust sits in the study where he was painted, into Westminster.

Watching a debate in the Commons Chamber, MacIntyre is the one loath to leave. "It was funny seeing people in there like Malcolm Rifkind, who were at my dad's funeral, and I've never met them," he says afterwards on the terrace, where Benn can smoke his pipe. Aged 36, with a bush of hair and heavy eyebrows, MacIntyre shares Benn's youthful, undimmed urgency.

"The theme of paying attention to the human was the driving force of the album," he says. "I thought, I'd rather have someone who represents what the words are about. Also," he turns to Benn, "your voice – I didn't want to tell you because you might think I'm stalking you. But I wrote a poem when I was a student called Tony Benn's Voice. I brought it for you..."

"Oh well, that's lovely," Benn says, and starts to read: "Tony Benn's voice/ Spills like coal off a truck... Oh, how very nice," Benn says, touched. "Oh, that's very sweet of you. You must sign it for me."

"It's a great voice, like William Burroughs'," MacIntyre says after we leave his teetotal hero for a nearby pub. His own career has been one of Benn-like, cussed individuality. Mull's close-knit community fed into the songs about asylums, islands, underdogs and losers on Loss and its follow-ups, Us (2003) and This Is Hope (2004). Mull Historical Society was a communal ideal as much as a band, an implicit refusal of Thatcher's disbelief in "society". Reverting to his own name, The Water is MacIntyre's most direct, pop expression of his curious world.

He is working on a novel about British soldiers' beliefs in wartime, and a "raw, Rick Rubin/ Johnny Cash-style" acoustic album. "I'm recording in a studio in my old school," he says. "It did something different to me, going home. Even on The Water, using the sound of the Tobermory town clock, and Tony Benn, means something to me. It's important to have those connections in everything I do."

Ask just what Benn's presence meant to MacIntyre – what process it completed – and he can hardly stop. "I think of both my grandfathers, and what they believed in," he says. "They were real characters, and I sense a similar man in Tony Benn. He could come from the Western Isles, he could sit and tell the same stories. That's why something feels right about this. And then to transcend that, and to go to Parliament for the first time, and to watch a debate in the chamber..."

MacIntyre falters, then dives deeper into what today meant to him. "Because of the reach my father had with politics and politicians, I've always felt a personal connection with Parliament. Looking down in the chamber, seeing people I used to play football with, I felt slightly frustrated today. When my dad died, I used to think I'd have some sort of link to the next few generations of prime ministers. And that might just be grieving. I might just have wanted to feel that comfort of being part of his world. But going there today, I brought all my dad's... stupid things, that I'd never show anybody... but one of them is this monkey, that was on his desk at the BBC. I like to have it with me. It's hard to get underneath those emotions."

MacIntyre studied politics and history at college. But though seemingly born a political animal, pop was a deeper, terrifyingly literal calling. "I was convinced I had schizophrenia for a while," he admits, "because I heard a voice that I couldn't ignore or deny. I remember saying to my dad one time that I thought I had this radio in my head. I thought I was mentally ill, to be honest. That radio works differently now. I don't have to reach out to the Dictaphone at 5am to keep it quiet by recording a song. But it's still completely switched on. I always have a red songbook on the tour bus, like the Chancellor with his budget."

When MacIntyre first toured, he was on the Warner label and shared a bus with The Strokes. With the self-released The Water, he's on his own. It suits a songwriter with closer ties to the ideals of an 82-year-old unbowed socialist than to passing trends. "It's almost impossible not to be sold any more," he sings on his new album. Benn himself, earlier, said of his own long experience of not "selling out": "My father used to say, 'Dare to be a Daniel, dare to stand alone.'" Watching them meet for tea in the mother of Parliaments, pop and politics briefly look like honest trades.

'The Water' is out now on Future Gods; MacIntyre releases the single 'Be My Saviour' and tours in May ( www.colinmacintyre.com)