He was objectionably crass, crude, unfunny, striving, insensitive, narcissistic and lacked even a hint of self-awareness. And we all knew someone at least a little bit like him.

That was why Britain warmed to David Brent, the excruciatingly gauche character co-created and portrayed by Ricky Gervais in The Office, the innovative mock-documentary first broadcast on BBC2 15 years ago this summer.

Ironically, Gervais has become dazzlingly rich and famous on the back of the loser he played so well.

Rocky Gervais as the new wannabe rock star version of David Brent in 'Life On The Road'

Gervais won critical and popular claim as the Brent character in the office 15 years ago

This year, he hosted Hollywood's prestigious Golden Globes awards ceremony for the fourth time. His vertiginous showbiz ascent, which didn't really begin until he was 40, even propelled him into Time magazine's list of the world's 100 most influential people in 2010.

But here is another, more perplexing irony: the more successful he has become, the more Gervais appears to have taken on Brent's foibles.

It is a very strange phenomenon, yet inescapably true. In his new film, David Brent: Life On The Road, it is Gervais, no less than Brent, who is crass, unfunny and narcissistic, and evidently not sufficiently self-aware to realise it.

For those of us who loved The Office — and I count myself as a fan — the warning signs come early in the big-screen spin-off, which Gervais wrote and directed without former collaborator Stephen Merchant.

He hogs the limelight from the start, putting Brent firmly centre-stage and allowing the other characters hardly any worthwhile storylines of their own.

The narrative has Brent taking a sabbatical from his mundane sales job and forming his own band. He harbours forlorn hopes of becoming a pop star, just as Gervais himself did in the Eighties as half of the widely and by all accounts deservedly forgotten 'new-wave' duo Seona Dancing.

That's a perfectly sound comic premise. But when he takes the microphone and performs his embarrassing songs, you can see Gervais fancies himself as a singer and yearns to be admired just as much as Brent does, fatally undermining the comedy.

Moreover, he badly overdoes the glances to camera and nervous yelps, losing all the subtlety that so enhanced The Office.

Stephen Merchant co-created The Office but was not involved in the new film, David Brent: Life On The Road

Worse still, he makes Brent, who worked for a paper products company when we first met him in 2001, a sanitary towel salesman. It is like watching The Office rewritten by a fifth-former.

Or, to put it another way, it's as if the man-child David Brent has written the script, which in a sense he has.

So why isn't Ricky Gervais funny any more?

One reason is surely that he needs the clever mind and restraining hand of Merchant, yet the two men appear to have gone their separate ways, amid rumours of a bust-up.

If Life On The Road is anything to go by, then it was Merchant who was the true genius behind The Office. At any rate, he would doubtless have counselled against the film's relentless crudeness, and advised Gervais to develop other characters more, and to tone down the 'Brent-isms'.

Without Merchant at his side, there is nobody to tell Gervais to rein it in.

That's what happens in comedy, just as it does in every other sphere of entertainment, and for that matter in politics and business, too.

The more powerful a man gets, the more convinced he becomes that he knows best, and can do without the correctives that helped forge his success in the first place. And the more others are prepared to indulge him.

But it's not just a matter of ego, as monumentally large as Gervais's reportedly is. It's also a matter of creativity.

With Merchant, whom he met in 1997 at the London radio station XFM, Gervais gave us not just The Office, but also Extras, the sitcom which started in 2005 and audaciously turned a spotlight on to showbusiness itself, persuading the likes of TV presenters Les Dennis and Keith Chegwin to send up their own fading celebrity.

Not everyone loved the idea behind Extras. The ventriloquist Keith Harris refused a role, later explaining: 'I read the script and thought: 'This isn't clever writing, it's pure filth.' I turned it down. I'm not desperate.'

Nonetheless, Extras received considerable acclaim, and with Robert De Niro, Samuel L. Jackson and Kate Winslet taking part, it confirmed Gervais as comedy royalty.

The hit U.S. version of The Office supplied further endorsement. And An Idiot Abroad, a collaboration with Merchant and their producer from XFM days, Karl Pilkington, was genuinely hilarious. Even if that was mostly down to Pilkington's deadpan persona, it offered further evidence that Gervais could do no wrong.

But without Merchant, he could. And did. The first character for years that Gervais conceived on his own was Derek, in the eponymous 2012 Channel 4 series about a simple-minded care home worker.

Rebutting charges that he was poking fun at mental disability, Gervais protested that he was merely being 'truthful', and honouring a TV tradition that had also produced unworldly mummy's boy Frank Spencer.

Yeah? Gervais won hearts in The Office series about a manager of a Slough paper merchant

Gervais hilariously danced at a party in The Office television series broadcast by the BBC

The last-ditch attempt in the film plot to make the grotesque Brent huggably sympathetic is clumsy and absurd, says Brian Viner

But Some Mothers Do 'Ave 'Em was funny, and it belonged very much to the politically incorrect Seventies. Derek wasn't right for any era. Even at its best, it was cloyingly mawkish.

Indeed, Gervais, rather oddly for a man who specialises in the comedy of merciless cruelty and humiliation, has a weakness for saccharine sentimentality. Perhaps it reflects his love for the silent movie era.

It just about worked in The Office, when he and Merchant gave Tim (Martin Freeman) and Dawn (Lucy Davis) the ending we all craved for them. But in the cinema, the last-ditch attempt in the film plot to make the grotesque Brent huggably sympathetic is clumsy and absurd.

The same sentimental impulse made Derek as unpalatable as a cup of tea with eight sugars. But such was Gervais's stature in the U.S. that, almost unbelievably, he was nominated for a Golden Globe for his lead performance.

Of course, American showbiz types (and their hangers-on in the case of the Globes, voted for by the Hollywood Foreign Press Association) are suckers for a simple-minded hero.

They gave the 1995 Academy Award for Best Picture to Forrest Gump, don't forget, ahead of Pulp Fiction and The Shawshank Redemption.

But even more than that, they are suckers for a success story. And Gervais, the working-class boy from Reading who didn't make it until he was well into middle age, is indubitably that. They don't even seem to mind being abused by him from the podium at the Golden Globes.

If anything highlights Gervais's faltering sense of perspective about his own place in the comedy firmament, and the growing smugness that has infected his humour, it is his hosting of this awards show.

He manifestly adores being part of the showbiz establishment: witness (if you must) his cackling, chummy turns with Jonathan Ross on the latter's TV chat show, which are always nigh-on unwatchable.

But at the Globes, Gervais ridicules the stars as if he, by virtue of his English accent and wonky teeth, weren't one of them.

It was funny the first time. But then he started to boast that Hollywood was 'scared to death of me', radiating exactly the thunderous self-importance he was supposed to be savaging.

A s with so much else, he has overdone it. As one blogger has perceptively pointed out: 'He goes after everyone in showbusiness on the assumption that they don't deserve their success, but if you listen closely, the implicit end of every jab is: 'But I do.' '

Gervais in the new film which follows him touring with his band through towns west of London

I've interviewed Gervais twice. The first time, when he was promoting series one of The Office, he was likeable, smart, and engagingly excited to have hit the big time. We had lunch together and bonded over a mutual passion for Laurel and Hardy.

The second time, around five years later, he was much more full of himself, yet also exuded a kind of mock-humility.

He had written an episode of The Simpsons, casting himself, more or less, as David Brent.

'We were doing the read-through,' he told me, 'and the other actors, like Harry Shearer [the voice of Mr Burns], were interrupting themselves to do other characters, and I'm thinking: 'I'm going to do my weedy little homage to Brent in a minute, to show how versatile I really am.' '

Many a true word is spoken in jest. With the notable and pitiful exception of Derek, almost all the character-based comedy he has done since The Office has to some extent involved a re-heating of Brent.

That includes other people's films (Ghost Town, A Night At The Museum) and his own (Cemetery Junction, The Invention Of Lying).

Not that he's a one-trick pony. No, the belittling jibes he unleashes at the Golden Globes, and in his stand-up act, and on social media, make him a two-trick pony.

Once upon a time, they were decent tricks, too. It probably doesn't matter too much to him that they have both started to look dreadfully stale.