By Stephen Robb BBC Entertainment reporter, BBC News

Catchphrases include wheelchair user Andy's "I want that one"

Lucas and Walliams were reportedly brought together at the National Youth Theatre by a shared love of the duo from whom they inherited their crown, Vic Reeves and Bob Mortimer.

The Lucas-Walliams partnership already spans more than a decade, having begun with the stage show Sir Bernard Chumley and Friends, which they first took to the Edinburgh Festival in 1995.

They brought the character of the ignorant and snobbish ageing actor to television screens in 1999, in six 10-minute episodes of Sir Bernard's Stately Homes.

The double act gained a wider audience with Rock Profile, the spoof interview series in which they impersonated the likes of Sir Elton John, Dame Shirley Bassey and Shaun Ryder.

Waxwork dummies

But when their parade of grotesques, Little Britain, was first aired on BBC Radio 4 in 2001, no-one could have predicted the all-conquering phenomenon it would become.

Three subsequent television series have won three Baftas, spawned best-selling DVDs, a hit stage show, Madame Tussauds waxworks and numerous ubiquitous catchphrases: "Yeah but no but..."

Little Britain has won a host of awards since its 2003 TV debut

A Radio Times poll last year named Lucas and Walliams the most powerful people in TV comedy.

All of which seems to justify BBC One controller Peter Fincham's comment on the duo's new BBC deal, "I think they are worth the money," though he declined to name the sum.

Devotees of Little Britain favourites Dafydd, Emily Howard, and Lou and Andy can look forward to two Christmas specials of the sketch show, and a UK tour of the stage version starting in October.

The BBC says they are also planning a new sketch show for next year which could incorporate Little Britain characters, after which their contract would still have more than a year to run.

There is a sense they are not just entertaining us, they are entertaining each other Anna Gien Series editor, The Story of Light Entertainment

Anna Gien, editor of new BBC series The Story of Light Entertainment, says that like Morecambe and Wise and the Two Ronnies before them, Lucas and Walliams are creating "comedy magic for their generation".

"The greatest double acts have had this chemistry through their writing and their performing that produces some kind of magic," she says.

But the series' first episode examining the history of the double act also highlights how the often intense relationships can turn sour.

Separate projects

Former partners Rob Newman and David Baddiel recall part of a tour when the only time they spoke to each other was delivering their lines on stage.

Tommy Cannon and Bobby Ball describe a theatre run when they would turn away from each other if they passed in the corridor.

Perhaps most famously, the declining relationship of Peter Cook and Dudley Moore in the 1970s was painfully evident in their work as the increasingly alcoholic Cook verbally abused his partner.

Spoof interviews with performers like Abba featured in Rock Profile

The joint success of Lucas and Walliams inevitably brings more offers of work as individuals.

Lucas is to play Mr Toad in a TV version of Wind in the Willows, and is also starring in a �200m advertising campaign to publicise the switch to digital TV.

Meanwhile, Walliams this year appeared in the film A Cock and Bull Story, and also has a part in the forthcoming Angels and Virgins.

Perhaps not surprisingly, Lucas also did not join Walliams for his cross-Channel swim for Sport Relief earlier this month.

But both performers had in fact achieved some degree of success before their shared triumphs, Lucas on Reeves and Mortimer's Shooting Stars spoof quiz show and Walliams as a TV actor.

'Mutual respect'

"As individuals they both have had their own success, so when they come together they are not fighting for the limelight," says Gien.

She adds: "For every falling-out, for every double act that has fallen, where it has gone awry, there is a Morecambe and Wise, a Two Ronnies, that just keeps going.

"They prove that double acts can endure - that those relationships, those 'marriages', that chemistry, that meeting of minds can endure."

She says that Lucas and Walliams "have an admiration and respect and friendship that comes across in their comedy".

"There is a sense they are not just entertaining us, they are entertaining each other."