Happy 40th to art's concrete bunker

The Hayward Gallery, the brutalist concrete bunker next to the Royal Festival Hall built for a mere £750,000, is 40 years old this week. On Friday, the day of the anniversary, admission will be a symbolic 40p instead of the usual £10.

Guests expected tonight include Sir Nicholas Serota, Zaha Hadid, Grayson Perry and Charles Saumarez Smith, together with curators, writers, cataloguers and exhibition staff past and present.

The dozens of artists who took part in the Hayward Annual have been invited, together with those celebrated by monograph exhibitions, among them Anthony Caro (1969), Richard Long (1991) and Howard Hodgkin (1996).

Southbank Centre chief Jude Kelly and Hayward director Ralph Rugoff are hosting the party. "It's a thank you to everyone who has been involved with the Hayward since day one," said Mr Rugoff, a 51-year-old American who has made a name for himself as as critic and convention-breaking curator.

"We've asked artists to make birthday cards for us, which we'll pin on a clothes line round the gallery."

The birthday cake, made to resemble the Hayward, has caused a few problems. How can you turn Sixties sludgegrey modernist building into a mouth-watering confection? "At least two chefs have given up already," said Mr Rugoff. "They couldn't manage the awkward mix of angles and cubes and pyramids, so now we're just having one facade instead. It'll be carried in to a fanfare of brass band and drums and I'm sure will be spectacular."

Antony Gormley, whose statues dominated the London skyline last year in his work Event Horizon, is the most successful of the living exhibitors.

His Blind Light attracted 210,000 visitors to the Hayward, making it the fifth most popular show in the gallery's history (after Renoir, Toulouse-Lautrec, Leonardo da Vinci and Picasso), and the sixth best-attended exhibition in Britain last year, putting it in the same league as the National Gallery and Royal Academy. On Friday, the 40p entry price will enable visitors to see the Psycho Buildings show, curated by Mr Rugoff, in which 10 artists have taken over the gallery with huge installations.

They include Rachel Whiteread's eerie Village made of 200 dolls houses; an exploding room; a gleaming steel tunnel which snakes between two floors; and an alien, ransacked gallery.

Were this Tate Modern, which specialises in this kind of interactive razmatazz, queues would be round the building. In the past decade, however, the Hayward had been dogged by a loss of identity. Under Mr Rugoff this may be changing. Gormley's Blind Light put the gallery back on the critical agenda, as did recent shows such as The Painting Of Modern Life, Laughing In A Foreign Language, and now Psycho Buildings.

"The vital task with the Hayward is to take a lead from the building itself," Mr Rugoff said. "It defies expectation. It's unorthodox. That's liberating. People are always anxious in traditional museums: should I go here or there, have I missed a bit, what comes next? Here, anything goes."

Forthcoming exhibitions already bear his stamp: a multimedia Warhol show (from Amsterdam's Stedelijk Museum) in October, and next year an Ed Ruscha retrospective and an eclectic show curated by Turner Prize winner Mark Wallinger. Then Tracey Emin in 2010. Alongside an ambitious programme, Mr Rugoff 's dream is to establish a ground-floor entrance to the Hayward, which would give the place a prominence now impossible with its single, discreet entrance on an upper level.

"But we won't know if we can do this until plans for the BFI [British Film Institute] next door have been finalised," he said. "At the moment we're a bit like a treehouse or a spider's web - with several ways to access a single entrance. That's quite intriguing but not necessarily the best answer for making ourselves known."