“The largest group of old English musicians ever assembled” is what Mick Jagger sarcastically called it: “If it ever rains in London, you’ve got to come over and help us.”

On Wednesday’s phenomenal “12-12-12 – The Sandy Relief Concert” in Madison Square Garden, Chris Martin of Coldplay told the audience watching at home, “If you’re going to donate tonight, think of the average age of the performers and we’ll raise billions.”

It seems to me it was the crowning event in 2012, which was the year of classic rock ’n’ roll in the entertainment world – especially the year of rock’s gerontocracy. “12-12-12” – available worldwide to an audience of billions – proved it.

There have been, to be sure, great movies in 2012 – Kathryn Bigelow’s extraordinary “Zero Dark Thirty,” the year’s most absorbing and troubling film by far – opening Wednesday in New York, Chicago and Los Angeles (Jan. 11, in Buffalo). And “Les Miserables” arrives soon.

And on TV, Showtime’s singular “Homeland” ends its seasonal run Sunday after finally scoring the Screen Actors Guild nominations it was absurdly and stupidly denied last year.

But “12-12-12” was the icing on the cake of classic rock’s remarkable triumph in the Western world, living proof that dumb geezer rock jokes are for really bad radio teams.

The big story of the publishing world was the caravan of fat, juicy memoirs by rock royalty – Keith Richards, Rod Stewart, Pete Townshend, Neil Young – all of which have been reviewed admiringly by our pop music critic Jeff Miers (which appeared with a big biography of Bruce Springsteen, along with huge books about Jagger).

On Wednesday night, the living lions of rock’s British invasion joined Springsteen, Jon Bon Jovi, Eddie Vedder, Billy Joel, Alicia Keys, Dave Grohl, Kanye West, Martin and Michael Stipe to, in Steve Buscemi’s description of The Who, show a world in dimwit demographic lock step about pandering to “youth” that they were “perennial but ever-young asskickers.”

The heroes of the night were The Who, who did a full set, which helped explain the weirdly perfunctory two-song “wham bam” drive-by from the Rolling Stones. (But then, the eternally business-savvy Stones were, no doubt, reluctant to give away too much for free when they’ve got a big pay-per-view event hitting cable TV Saturday night.)

The Who’s set was a poignant and artfully megavolume horse laugh at mortality, with Roger Daltrey turning his back to the audience to do a duet with a film of Keith Moon, the band’s original drummer and eternal symbol of the music’s penchant for killing off those who are most drunk and disorderly.

The refrain on “Baba O’Riley” was changed for the money-raising evening from “teenage wasteland” to “Sandy wasteland.”

With Who bassist John Entwistle gone now, too, Daltrey and Townshend ended their set together in a duet with Daltrey singing they’d just have a cup of tea. To which Townshend’s hooligan soul couldn’t resist disagreeing with his musical partner in a final sarcastic coda “Have a f— beer.”

The show ended with Paul McCartney reuniting what’s left of Nirvana and copping off an evening of killer granddaddy rock that, intentionally or not, had the effect of showing its younger participants to be more than a little awed and a bit less than equal.

When I say that might not have been unintentional, it’s because one of the evening’s producers and masterminds was Harvey Weinstein, who is himself at putative geezer age (60) but coming back home to his first profession, rock promoter, which he did with such heedless and energetic panache in Buffalo before morphing into a great mover and shaker in world cinema.

By the time Harvey and his former partner Corky Burger finished in Buffalo, they left the venerable old Century Theater on Main Street a ravaged shell of its former self. And then Harvey and brother Bob compounded the crime in their film “Playing for Keeps” by concocting a putrid demographic us-vs.-them fantasy about righteous big city youth trying to bring a rock ’n’ roll hotel to a community full of sclerotic bumpkins.

You can’t turn a grotesquely snotty and bad attitude into a felony, but if you could, Harvey and Bob’s “Playing for Keeps” would be Exhibit A, along with pictures of the Century Theatre by the time they finished with it.

Time and mortality, though, change everything.

The Harvey Weinstein who produced “12-12-12” is a great film world figure and force for philanthropy and progressive politics, not a living symbol of urban despoilment on Main Street.

It was impossible, though, for me to watch “12-12-12” and not think that Harvey wasn’t merely reliving his own glory days as a rock promoter, he was fulfilling them by giving the world – for the worthiest possible cause – some astounding life triumphs in music that paralleled his own triumphs outside music.

The evening’s opening act was Springsteen, who brought fellow committed Jersey boy Bon Jovi out to sing “Born to Run” with him.

Then came Roger Waters, and all I could do was remember reviewing Pink Floyd at the late, lamented Peace Bridge Exhibition Center in a show promoted by Harvey and Corky’s main Buffalo competition, Jerry Nathan’s Festival East. (Nathan, afterward, answered my questions about attendance that night in a locked box office containing more cash than I had ever seen before or since.)

After reaffirming his eternal opposition to “dark sarcasms in the classroom,” Waters brought out Pearl Jam’s Vedder to be “Comfortably Numb” with him.

But mostly Waters proved, like so many of the night’s British stalwarts, how magnificently hardy their generation remains.

They came to Madison Square Garden, with Harvey’s help, all thin, wiry and gray-headed, ready to rock the Garden down to its foundation and put on a show.

That’s what The Who did better than anyone, with the consequence that Daltrey, in particular, put himself back on the musical map. While his old pal Townshend was still windmilling his guitar chords, Daltrey, at the age of 68, was putting his voice through the kind of stadium/arena rock workout that Led Zeppelin’s Robert Plant, for one, has proved largely unwilling to do anymore.

I loved Eric Clapton’s three-song trio blues update of a set by Cream, beginning with an acoustic “Nobody Knows You When You’re Down and Out” and ending with Robert Johnson’s “Crossroads.”

I never thought that Clapton in his prime was God. But as I watched him Wednesday night coming out with his Brit rock generation for such a great American cause, I thought that just maybe, he’s a little bit holy.

Madison Square Garden was their house Wednesday night.

A great moment in a great year for rock.