Extras returned to our screens at Christmas for a one-off feature-length episode featuring special guests George Michael, Clive Owen, David Tennant and Gordon Ramsay.

The Christmas special saw the return of Andy Millman (Ricky Gervais), who has become a big star with a hit TV show and a brand-new, hot-shot agent to replace the hapless Darren Lamb (Stephen Merchant). 

Andy has achieved fame and fortune, but respect and acclaim are proving as elusive as ever and his discontent is growing. Best friend Maggie is finding this hard to fathom, as her luck has gone from bad to worse and she's on the breadline doing cleaning jobs to make ends meet.

Gervais and Merchant created Extras whilst exploiting the fame and contacts they had generated through the popularity of The Office.

They created a more ostensibly glamorous background for their next effort, whilst deciding to remain on BBC TWO for the first two series, rather than the more exposed and scrutinised senior channel: they weren't going allow themselves to be built up for a fall.

In series one, Gervais gives a refreshingly low key performance as Andy Millman, a man down on his luck and who has none of the oafish bluster of his Slough based doppelganger.

Andy starts out as an actor reduced to doing extra work on film sets; frequently alongside his daffy, well meaning but socially naïve friend Maggie.

Though Maggie frequently lands Andy in trouble (mistakenly convincing one production team that they are racists, almost losing him a BBC writing commission) theirs is a low-key and rather sweet bond and Andy's principal problems are caused by his catastrophically dim agent: Darren (Merchant finally emerging from behind the camera and proving just as able a comic performer as his cohort).

Said agent was the thorn in Andy's side: lining him up with soul destroying work or mucking up existing arrangements, usually by trying to get his other visible client 'Barry from Eastenders' (Shaun Williamson in a winningly self-effacing performance which will get him canonised should sainthoods ever be doled out to comedy actors) a slice of the action.

The initial pull of each episode is seeing how this week's star cameo will work: the obvious comedic potentialities of seeing a cowardly Ross Kemp, a childish and boastful Daniel Radcliffe and a sleazy Patrick Stewart are delivered with self-effacing panache by the guests.

Despite appearances from Kate Winslet and Samuel L Jackson, though, the most memorable episode of series one features Les Dennis, capitalising upon his media image as a broken man, unravelling to the point of nervous breakdown.

Extras is about failure as much as success.  Keith Chegwin reinventing himself as a bitter, racist halfwit in series two is a similarly bravura turn.

Rather than trot out the same formula for the second series, Gervais and Merchant instead had Millman taste some form of success with the leading role in a sitcom he has written.

Andy's frustrations continue though, as instead of creating something of genuine worth, constant tinkering by producers and directors dilutes his vision and his high-concept ideas are reduced to characters in wigs falling over and issuing catchphrases.

Although in reality no extra would ever rub shoulders with the stars to such an extent and Andy would surely have sacked his agent the minute a whiff of success occurred, this series is so much more than the back-slapping showbiz event many feared it might be.

For all his faux boastfulness at award ceremonies, Gervais clearly thinks carefully about where to pitch his comedy and success has not diluted his ability to get to the nub of human  frailty.