Until Evan Almighty dampened everyone’s spirits, writer Michael Ian Black was responsible for the least amusing comedy of 2007: the abominable Wedding Daze.

And as co-conspirators in the so-so crime farce Big Nothing, Simon ‘Shaun of the Hot Fuzz’ Pegg and David ‘forever Ross’ Schwimmer could hardly be deemed a winning team.

Fortunately, with Schwimmer opting to stay behind the camera and Pegg whipping Black’s original Fat Boy script into shape (swapping its New York setting for London), the trio are back on the right comedy track.

We meet Pegg’s loser Dennis in the throes of a panic attack. He is due to marry the gorgeous Libby. She is due to give birth to their son. He duly legs it.

Fast-forward five years and Dennis is a fag-smoking, behind-on-the-rent loser who works as a security guard in a lingerie shop. Potential shoplifters have it easy.

Still holding a torch for Libby, he at least makes the effort to be a good dad to young Jake. But now there’s annoyingly healthy competition in the form of Whit (Azaria), Libby’s buff and ultra-successful American beau.

The prospect of losing the life he should be living to a smart, handsome and (in every sense) well-endowed Yank is too much for Dennis. Determined to prove that he’s worth more than a Whit, he rather rashly vows to run the upcoming marathon.

‘Coached’ by his best mate Gordon (slacker supreme Dylan Moran) and distinctly unathletic Indian landlord Mr Ghoshdashtidar (bless you!), Dennis hits the streets like a cross between Mr Bean and Rocky.

From training pratfalls to Whit’s inevitable public proposal and subsequent fall from grace, Schwimmer never allows Fat Boy to stray from the comedy underdog template.

But the pace rarely sags and Dennis is thrown into enough daft, embarrassing and – as evinced by the blister-popping scene - eye-watering situations to induce at least a couple of big guffaws.

Newton isn’t required to do anything but look lovely in another of her patented partner/mother roles but Pegg and Azaria play off each other nicely, and the rest of the cameo-crammed cast (The Fast Show's Simon Day, Stephen Merchant, David Walliams, Play School's Floella Benjamin...) provide fun in support.

They add almost as much swoosh to proceedings as the world’s largest sportswear label, which benefits from the most shameless product placement deal since Popeye shook hands with the American Spinach Association.

Fat Boy’s message couldn’t be simpler: just do it.

Elliott Nike