Matthew Sweet examines the success of Channel 4 television as it prepares to celebrate its 25th birthday. What was the spirit in which it was created, and has it lived up to its early promise to serve minority groups in Britain? Matthew's guests include writer and former commissioning editor Farrukh Dhondy, the former director of programmes Liz Forgan, and the Guardian's media correspondent Maggie Brown who has written a history of Channel 4.