In the film of the Rolling Stones' 1968 Rock And Roll Circus, the summit of Sixties superpowers in which The Beatles, The Who, the Stones and Eric Clapton gathered in a television studio, there's an excruciating moment which encapsulates the Yoko Ono Problem.
A scratch band called The Dirty Mac, comprising Clapton, Keith Richards, Mitch Mitchell and John Lennon are jamming away when Lennon's fiancée wanders on stage. Ono begins caterwauling for what feels like aeons, much to the musicians' evident discomfort. No one can meet the Beatles' gaze, but their expressions say it all: we wouldn't be putting up with this nonsense if she weren't Lennon's missus.
There's been a lot of misogynist rubbish written about Yoko Ono, much of it based on the questionable idea that she was a manipulative gold-digger who single-handedly "split up" a band who couldn't stand one another. However, there's also been a tendency to proclaim her as an unsung genius. She is, of course, neither. Independently wealthy, she was a mediocre avant-garde artist with a knack for convincing people she was something more. And so it remains.
Probably the kindest thing to be said about her revived Plastic Ono Band is that she's created a space in which avant-garde things are allowed to happen, and of which she herself is the least talented component.
In trademark shades, she fronts a majority-Japanese line-up containing members of Cornelius's backing band, Yuka Honda from Cibo Matto, Mark Ronson, and her son Sean Lennon. Much of tonight's set, culled from Ono's 40-year career, amounts to a cacophony of diarrhoeic Expressionist rubbish, and film of a housefly buzzing around a naked body sums up Ono's irritant factor all too accurately. Frustratingly there's no "Walking on Thin Ice", but there is, for pity's sake, a song Sean wrote for her when he was 17. Rarely have the words "this is a song from my mom's next album" sounded so ominous, especially when followed by "... she wrote six songs that day".
Lennon introduces guest Antony Hegarty with some awkwardness ("He's a man who ... he's a woman who ..."). When she starts screeching and cackling like a chimp in a hot bath, the gentle giant regards her with kinder eyes than the musos did back in 1968.
Yoko's still waffling on about her love-hate relationship with Britain when an elderly gent in a leather trilby and two-tone suit shuffles on. This is Ornette Coleman, the legend who played on Ono's 1969 debut, and is curating the Meltdown festival of which this show is part. To hear him play his white tenor sax on 1971's "Mind Train" is, even to someone as phobic of free jazz as I, electrifying, and no less so because his instrument is, throughout, a semitone sharp.
The red silk banner hanging above the stage of the Blackwood Miners' Institute bears the motto "Forward to a Socialist Britain and World Peace". Both those dreams seem further away in 2009 than they did a quarter of a century ago. The miners' strike was a formative experience for anyone who witnessed it. Growing up 25 miles from Blackwood, I remember NUM collection buckets being shaken in my town. For a while, it genuinely felt that revolution was in the air. Billy Bragg understood. "I was a miner ..." were the first words most people heard him sing, channelling an everyman who voted "not for the iron fist, but for the helping hand" on the moving and hymnal "Between the Wars" (a "Jerusalem" for comprehensive kids).
At the end of a Welsh tour to commemorate the 25th anniversary of the strike, he's back to "reconnect with the spirit of collective action" in the place where the strike was strongest. Bragg is preceded by locally based poet and playwright Patrick Jones (elder brother of Nicky Wire), a passionate and often hilarious performer who takes on bigotry, environmental destruction and organised religion.
The headliner rattles through Eighties favourites ("A Lover Sings", "Sexuality", a singalong finale of "A New England"), Dylan and Carpenters covers, Woody Guthrie songs, and spins stories about being mortified to discover George Osborne is a fan, and generally stakes a claim for his place as an Old England Springsteen. At least three times, Bragg brings absolute shivers. One is "Between the Wars" itself. Another is "Levi Stubbs' Tears", his heartbreaking mini-drama. The third is "Which Side Are You On?", his apposite adaptation of the 1930s American folk standard, with the stark stanza "It's hard to explain to a crying child/Why her daddy can't go back/So the family suffer, but it hurts me more/ To hear a scab say 'Sod you, Jack.'"
In a week when election results improbably turned Wales blue, Bragg and Jones are doing their part to eradicate apathy. But for now, Blackwood – like the rest of the country – is still waiting for the great leap forward.