Hadrian Piggot makes sculpture out of soap: washbasins made of soap, shrink-wrapped soap casts of the interiors of baths, rows of hand-soaps, stamped with the name of a part of the body. These slippery monuments to the artist's bathroom fixation are momentarily amusing, but their scale doesn't survive the Saatchi treatment, the echoing acres of empty floor, the vastness of the white void. Piggot's work suits a more intimate space, but here he's a one-line comedian playing to an empty hall.
Keith Coventry's crusty, white-on-white paintings are derived, ultimately, from the meticulous work of Robert Ryman, conflated with a half-mocking use of hessian borders and glazed frames - the over-dressed, retro look of 1950s Modernist chic. These impasto paintings, with their ghostly, lumpy images of the last debutante, the Changing of the Guard and "Sir Norman Reid explaining Modern Art to the Queen" (a title that immediately brings to mind Joseph Beuys's famous lecture to a dead hare), want to have it both ways. They ask to be taken seriously as paintings and as conceptual jokes.
Flattened, distorted trompe-l'oeil versions of Salvador Dali, Frank Auerbach and Asger Jorn, Glenn Brown's works are familiar double-takes on the problem of originality. Lately, he has taken to painting blown-up versions of the sci-fi comic book illustrations of Chris Foss: wrecked space-stations and interstellar factories, asteroids and solar flares. They are like the bedroom wall posters of pre-teen space cadets. Brown piles on the strata of meaning like layers of filo pastry, giving these paintings complicated titles that refer to works by other artists. He is also showing some gnarled lumps of paint and plaster on low plinths, looking like dried-out scrapings from an expressionist's pallette.
Kerry Stewart's life-sized figures come close to the simplified lumpen aesthetic of the figurines that people model railway sets and toy farm layouts. There's a bedsheet ghost, a sleeping nun, a pair of twins, a pregnant schoolgirl and one of those mawkish papier mache boys that used to plead for pennies for the Spastics Society outside chemist's shops. They all work well enough as images, but have no sculptural presence whatever. Maybe, once again, it's the space that kills them.
n Saatchi Gallery, London NW8 (0171-624 8299) to the end of the year