The final episode opens in the late seventies as observational comedy blossoms thanks to an Englishman, a Scotsman and a Welshman. Listen out for the birth of comedy clubs too, and more...

Seventies escapism gave way to Eighties cynicism, and this final episode explores why comedy changed suddenly instead of gradually - and the role Channel 4 played in that change.

This was the era of The Young Ones and Blackadder, but was alternative comedy really something new? Post Second World War, the old order was actively challenged by those seeking a new approach and even before that, the Crazy Gang had almost set the template for 'alternative'.

Part Four looks at the Nineties and beyond when stars who'd grown up on their new wave predecessors also saw the best of what had gone before them. In a time when the nation's divisions were less obvious, so it was with comedy.

And as ever - there was change. The programme hears about stadium stand-up, sitcoms without laughter tracks, and big-screen comedy successes.

David also asks what new methods of communication will mean to British comedy - new portals for the latest experimental live improvisational sitcom featuring a cast of train spotters, or opportunities for comedy consumers to discover new laughs in classic clips. Via YouTube and its ilk, new audiences are discovering long-dead comedy greats in a way that that suits their needs - Tommy Cooper material in particular has a high hit-rate amongst those born since he passed away.

Among those featuring in this episode are Michael Grade, Denis Norden, producers Beryl Vertue and Johnnie Hamp, writers John Sullivan, David Nobbs, Carla Lane and Barry Cryer, showbusiness agent Laurie Mansfield, co-founder of The Comedy Store Don Ward, media lecturer CP Lee, expert on British film Steve Ellison, Alan Davis, Jimmy Cricket and Dave Spikey.