The Koestler Awards Scheme, which is dubbed the Turner Prize for prisoners, is more than just an unconventional art prize. It's a scheme that really helps turn offenders' lives around. And this year, just as it sees a withdrawal of its government grant, it's been given an unusual boost: instead of having to go to Wormwood Scrubs, you can find many of the entries at no less a venue than the ICA.

The selection on display has been chosen by a panel that includes Grayson Perry, an artist whose own work is very much inspired by outsider art - that is, art by prisoners and psychiatric patients. Such work has had a huge influence on the development of modernist art, so it's certainly interesting to see that influence feed back on the prisoners themselves. You'll find, for instance, Dubuffetlike graffiti scrawls scratched into the surface of thick paint, as well as obsessively detailed drawings. Garvey Thompson's two engaging 'naive' selfportraits (pictured) are just a couple that stand out.

The overall standard of work is genuinely impressive, especially in Perry's own medium, ceramics. Indeed, Perry seems to have a particularly strong following among the prison population. We find inscribed pots, grim puritan figures on church pews and ghoulish puppets.

This is a very affecting exhibition - and not just because it's in the name of a good cause.

Until Sep 9, ICA, The Mall SW1, daily noon to 7.30pm (Thu to 9pm), Mon to Fri £2, £1.50 concs, Sat and Sun £3, £2 concs. Tel: 020 7930 3647. www.ica.org.uk Tube: Charing Cross/ Piccadilly Circus