Journalist Toby Young has a reputation for being an obnoxious cad with few likeable qualities - this is a man who brought a stripper to the office on Bring Your Daughter To Work Day. So reinventing Young for a big-screen version of his memoirs How To Lose Friends & Alienate People meant the star had to be innately funny and likeable. Enter one of the UK's hottest home-grown actors, Simon Pegg.

'People who know Toby or have read the book, asked, 'How do you make this character sympathetic'' The answer is Simon Pegg,' says the film's director, Robert Weide. 'When I got the script, I was vaguely aware of Simon from Spaced. Then I saw Shaun Of The Dead and I knew this was our guy. Now I can't imagine this film without him.'

'I've never worked with someone with such comedic talent,' adds Stephen Woolley, who produced the film with his Number 9 partner Elizabeth Karlsen.

Pegg himself says: 'It was such a good role, he's such a scrupulous character. He's an idiot but he's lovable. The script was really funny but it also has these moments of tenderness.'

And working with Weide, renowned for directing Curb Your Enthusiasm as well as comedy history documentaries, was a draw for Pegg: 'I'm such a huge Curb fan, so I was able to geek out with him a bit. As a director, Bob is very empathetic and he also knows comedy really well. You need someone funny helming the characters.'

Of course, the film is about more than Pegg. It started with Young himself, whose 2003 memoir about his years as a misfit English journalist trying to work his way into New York's hottest magazine was a bestseller. Karlsen loved the book and passed it to Woolley. 'I was just reading it casually, not with an acquisition in mind, but it really made me laugh,' Woolley says.

But the rights had gone to the previous incarnation of Film4, then headed by Paul Webster. When Film4 was dismantled, Number 9 wanted to become involved and entered discussions with Young and the new Film4's head, Tessa Ross. Soon, Intandem was also on board.

Young wrote a treatment which Woolley says was 'terrible' so they knew they had to get an outside screenwriter to tackle the source material. Peter Straughan was the man for the job.

'We knew it was important to take off from the book, with this we had to create more of a spine for the story,' Woolley says. 'It's turned into a His Girl Friday-style romantic comedy, and that helped to structure Toby's experiences.'

In the film, Toby is Sidney and the magazine becomes Sharps, not Graydon Carter's Vanity Fair. Instead of just re-counting a series of Toby/Sidney's mis-steps (such as sending a strippergram to work or bringing a pig to a party), the film has much more of a story arc than the memoir.

Sidney finds a confidante at work (Kirsten Dunst) as well as a rival (Danny Huston), tries to charm a Hollywood starlet (Megan Fox) and rubs his new boss (Jeff Bridges) the wrong way.

'I knew we needed someone who could direct comedy,' says Woolley of the hunt for the right person to direct the script. Number 9 had its sights on a US director 'because they would understand how Americans would deal with a character as weird as Toby Young/Sidney'.

Weide, a fan of comedy in the vein of the Marx brothers and Preston Sturges, was still busy with Curb Your Enthusiasm when he received the script. 'I wanted to do a feature film for a long time, but I was determined to find the right thing,' he says. 'You can recognise good writing on the first page, and I felt that right away with the script. I thought, 'This is exactly what I've been waiting for.''

After working on a largely improvised TV show, he says: 'One of the pleasures of this film is having a script and thinking about shots and coverage and planning edits and transitions.'

Working with his cast was also a highlight. 'I really enjoy talking about motivation in characters, so we had a lot of those discussions in rehearsals and worked things out,' he says. To fully appreciate how much actors 'go out on a limb', he has a one-line role himself as a journalist at a July 4 party.

Film4 and Number 9 developed the project with early backers Intandem, which also handled international sales, and with backing from the UK Film Council's Premiere Fund, finance powerhouse Aramid and post company Lip Sync's new features department. Paramount came on board for UK/Australia/New Zealand rights early on; and MGM now has US rights (both are launching October 3).

The $27m film shot in summer 2007 for 54 days, at London's 3 Mills Studios and on location for two weeks in New York at iconic places such as the Brooklyn Bridge, Hell's Kitchen and the rooftop pool of Soho House.

Woolley says Weide and the cast adapted well to shooting in the UK. 'In the US there's a certain amount of hysteria on sets, there's much more incessant information passing,' Woolley suggests. 'But it's human nature here in the UK that we just have more of a steadiness and calmness about us.'

Woolley has of course been a long-time producer and has also directed Stoned. So was he tempted to hold the hand of his first-time feature director' No. 'I'm trying to enable Bob to make the best film he can make. Bob is our director. I know we got the right director because Bob really enjoys making people laugh. That's what I wanted from the film - to make it really funny.'

Buyers are certainly getting the joke; Intandem has sold widely, thanks in part to the strength of the cast. 'Simon Pegg is untouchable in comedy in the UK,' says Intandem's Gary Smith. 'The three films he's made have had relatively modest budgets and have still made an average of $30m at the box office. This film could be the one that breaks him out even more into the mainstream. We think it will be a real breakout.'