Everyone is so post-gay now, it's probably not the done thing to shed a tear over the last night of G-A-Y at the Astoria in Central London this Saturday. With its simple delight in fluffy disco and boozy, cruisey merriment, G-A-Y seems a dinosaur in the modern landscape of gay indie clubs, mixed clubs and the pansexual, drag-tastic dives of Shoreditch, where the beestung-lipped boy in eyeshadow probably has a girlfriend who's cool with it all.

But sad I am for the passing of G-A-Y. Jeremy Joseph, the club's pixie-like promoter, says it will reopen somewhere else, but it won't be the same - for good and ill, for its fans and detractors, G-A-Y at the Astoria is a gay cultural landmark, and even though it smells of chips and the Astoria has seen better days, the club has a resounding pre-eminence. While Joseph's G-A-Y has been going since 1993, the night began life as Bang! way back in 1976. It's a gay grand-daddy in a tight T-shirt.

As the club's capital-lettered, branded moniker implies, G-A-Y is gay and then some. It doesn't try to be clever or jaded. Instead it serves up, weekly, a cacophonous, fizzing party, the centrepiece of which is a performance by a pop star. Madonna, Kylie, Mariah Carey, Cyndi Lauper, Pink, Enrique Iglesias (and a lot worse - step forward Caprice) have appeared at G-A-Y: Iglesias generously offering up his ass to be fondled. Joseph doesn't think that the G-A-Y brand is outdated: “We've survived longer than any other gay club. Does that sound unsuccessful to you?”

G-A-Y encompasses not just the Saturday-night club but also two Soho bars. Along with Heaven, it is the first, most visible homo port of call not just for foreign visitors but for 16-year-olds coming out. Its young crowd sets it apart: if you are over the age of 25 you feel ancient.

Joseph says that he has decided to ship out because he is fed up with having “the axe of Crossrail hanging over my head”. He still doesn't know if or when the Astoria will be knocked down to make way for London's high-speed rail link, but this week Crossrail received Royal Assent, which Joseph took to be “a message - the time is right to go”.

Joseph says that it is getting harder and harder to show stars around the building when it's in such a bad state. But he'll be emotional on Saturday night, he admits - his energy and ability to get stars to perform at G-A-Y have given the club an enviable profile. Open the tabloids on a Monday morning and there will be a picture of, say, McFly dropping their pants on stage.

The most dramatic appearance was possibly that of Kylie Minogue on stage, post-cancer operation, alongside her sister Dannii. That night I had been out at Ghetto, just behind G-A-Y, and was accosted by two sweet and breathless young guys on the night bus, eager to share the news (and pictures taken on their mobile phones). Over the years, G-A-Y has played a part in mobilising support for significant gay political campaigns, such as Section 28, the age of consent and gays and the military.

Joseph has had many messages from G-A-Yers young and old in the past few days. “It was the first place they went to when they came out - or before they came out; the place they went to be themselves if they were having problems with families or colleagues. I've even had messages such as ‘I met my boyfriend ten years ago at G-A-Y. If you hadn't been there we'd never have met'.”

Joseph won't say where or when the club will reopen. He is being very cagey about what will happen on Saturday night, too. “Lots of acts” will be performing - he says that Kylie and Madonna are unavailable, but is this a decoy?

The evening isn't about the “names”, he says strenuously, or he would publicise them. It's about saying farewell to the club. All will be revealed when the show starts at 1am. Joseph will make a speech - “I've been trying to compose one on the running machine but I keep getting stuck” - and a grand finale (prepare for glitter guns and tears) is planned for 4.15am.

For Joseph - and me, it turns out - the song that best sums up G-A-Y is Kylie's Better the Devil You Know. For the past 15 years he has played it at 12.30am each week.

“It's one of the world's best pop songs,” he says with absolute authority. “When you hear that first ‘Woo-ooohhh-ohhh' in the opening bars, you just know...” And his voice tails off but I know what he means. Jeremy, see you on the dancefloor at 12.30am.

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