YOU HAVE TO GET IN. That is all that matters. No wonder, then, that Hollywood’s more inventive minds go to such amazing lengths to make sure they get on the right side of the velvet rope for the all-important postOscar party.

Perhaps the most celebrated attempt at gatecrashing was in 1996, the year that Babe was up for an Academy Award. “These people arrived at the Vanity Fair party in a stretch limo with a pig. They were swept in,” recalls the showbusiness photographer Dafydd Jones. “But they were just journalists who had decided to gatecrash all the parties.”

Once you are past security, nothing, not even imminent death, is judged by the Hollywood establishment to be sufficient reason to opt out of the jollities. Shortly before he died, John Huston turned up at the legendary Oscar- night party thrown by über agent Swifty Lazar. The great director was “sitting there with an oxygen tank,” one Hollywood habitué recalls.

Post-Oscar parties are a de facto extension of the awards ceremony, and attendance is a barometer of one’s status. For that we have to thank Lazar and his annual celebration party at Spago, the fashionable restaurant. His party was more than the most important in town — it was the most important all year.

Johnny Gold, the founder of Tramp, had a branch of his nightclub in Los Angeles during the 1980s. “There was nothing to match the little maestro,” he says. “Swifty’s party was so hot that, in the words of Jackie Collins, if stars were not asked they put the shutters down and pretended they were out of town. You would turn up there in black tie at half past five and sit down with the sun still high in the sky.”

After the ceremony, Oscar nominees and winners would swing by. “When you saw these stars come in, a roar would go up like a cup final,” Gold recalls.

“People were terrified of Swifty Lazar,” remembers Jones. “They would go to his parties because they would be scared not to. He used to stand near the door with his walking stick and poke me to make me take pictures of him with the stars.”

Lazar’s parties ended a decade ago, after some 20 years, when the agent died. But in 1994 Graydon Carter, the Editor of Vanity Fair, decided to fill the vacuum and, with the film producer Steve Tisch, threw a party at Mortons, a fashionable restaurant on Melrose Avenue.

“In Los Angeles there are certain nights of the week for certain restaurants and at that time it was Monday night for Mortons,” says Beth Kseniak, a Vanity Fair spokeswoman. “It started out as a small dinner party and has grown organically.”

It also survived an earthquake in 1995, and two power cuts last year. Invitations are sent out on the same day as the Oscar nominations, and within a week there are three binders full of faxed requests for invitations from those who feel that there must have been some oversight or their invitation was lost in the post.

The guest list is restricted to denizens of Tinseltown. There is often a “notorious” guest: one year it was Monica Lewinsky, another time it was Anna Nicole Smith, and people still talk of the year that Pamela Anderson and Liz Hurley did a little floorshow (Liz has not been asked back).

The party is now so big that Carter’s architect is flown out annually to demolish one wall of the restaurant, to allow access to a tented annexe. After the party the wall is rebuilt.

The first wave of 130 guests sits down for dinner to watch the ceremony. (Last year’s menu started with an avocado and endive salad, followed by steak, striped bass or macaroni cheese, and finished with frozen cheesecake parfait.) After that, guests start arriving at carefully timed intervals — the party is at its busiest between 10.30 and 11pm — with the least prestigious guests given the post-11.30 slot.

Despite LA’s reputation for healthy living and early bedtimes, the party continues until one or two in the morning. More shocking still, some people drink and smoke — each dinner guest has a Vanity Fair Zippo lighter by their place.

Naturally, Vanity Fair is not the only stop-off on such a crucial night. The Governor’s Ball, staid but important, is the first fixture on the night, although one regular partygoer dismisses it sniffily as “very trade”.

The two biggest studio parties this year will be those thrown by Paramount and Miramax — although the mood at these events will be governed largely by who wins what on the night.

The proximity of the parties makes it possible for guests to commute with ease between venues, maximising media exposure and minimising time spent stuck in limousine jams.

The lively post-Oscar party scene is now influencing showbusiness partying in Britain, where post-Bafta bashes are moving up a gear or two. “If you look at the attendance over the past few years, Hollywood is taking Bafta much more seriously and the dresses are getting almost as much attention as in LA,” says Lynda Fletcher, of the party planner Hyperactive, who has arranged revelry for Harvey Weinstein, the co-founder of Miramax: “For the post-Bafta parties we have done in London, having Harvey Weinstein as host makes a lot of difference. You get guests like Dustin Hoffman, Kevin Spacey and Mick Jagger.”

But a post-Bafta party is a more relaxed affair than its cousin in LA, according to Fletcher: “At one point one year, Dustin Hoffman disappeared,” she recalls. “We found him in the kitchen cooking scrambled eggs for the staff.”

Times recommends

• Lindsey Bareham’s week in recipes
• What I ate yesterday: Hardeep Singh Kohli
• Six of the best value Chilean wines