Run, Fatboy, Run (2007) on Netflix

Clumsy, lazy London boutique security guard Dennis left Libby, the mother of doting and adored five year-old Jake, at the altar. Now that she has a new lover, hunky American business executive Whit, who takes an active interest in the boy, Dennis fears to loose Jake. Hearing Whit is training for another marathon, Dennis hopes to prove himself worthy. Getting fit would fail utterly, hadn't his dodgy mate Gordon wagered on him against his dangerous gambling debts, while Dennis's Indian-roots landlord Goshdashtidar volunteers as 'assistant coach', armed with a motivational ladle. It's a miracle they even get Dennis registered, too late, needing a sponsor. That done, the race proves eventful, and reveals Whit isn't as perfect as he looked naked in a gym locker-room as well as an engagement party.