What is 'Outsider Art'?

The BBC's arts editor Will Gompertz asks what is Outsider Art and why it has become more fashionable.

A new exhibition is opening at the Hayward Gallery in London called An Alternative Guide to the Universe and features the work of so-called Outsider Artists - who happen to be very fashionable in the art scene.

First broadcast on BBC Radio 4's Today programme on Tuesday 11 June 2013.