Almost 20 years ago, Rob Reiner’s seminal romantic comedy When Harry Met Sally... posed the age-old question: can men and women truly be friends without sex getting in the way?

For Meg Ryan and Billy Crystal, carnal desires wrecked their characters’ friendship, reducing a previously rock solid relationship to a morass of anger, regret and razor-sharp one-liners.

Writer-director Kevin Smith considers the very same question in this hysterical relationship comedy, which is every bit as filthy-minded and profane as the title suggests.

Yet for all the obscenities and perversity, Zack And Miri Make A Porno is incredibly sweet and romantic as it brings together two best friends who love one another – but don’t yet realise it.

This is truly a return to sparkling form for Smith; a zesty and salacious companion piece to Clerks and Chasing Amy that manages to walk and talk sex without seeming sleazy.

The characters are willing and impressively able participants in the sauciness, so we laugh with them not at them as they overcome budgetary restrictions and myriad misfortunes to give their all in the name of low budget enterprise.

The smoldering screen chemistry between lead stars Seth Rogen and Elizabeth Banks is a key factor.

Whether their eponymous misfits are behaving like drunken fools at a high school reunion or wreaking havoc in a bathroom that has just run out of running water, we adore them and wait expectantly for the moment destiny opens their eyes to their true feelings.

Childhood pals Zack (Rogen) and Miri (Banks) can’t afford any of their utility bills and are months in arrears with the rent.

In a moment of genius masquerading as desperation, Zack hits upon a novel solution to their cash flow problems: they could make an adult film.

A rag tag film crew including a gun-chewing cameraman (Jess Anderson), impressively proportioned leading man (Jason Mewes), brazen co-star Bubbles (Traci Lords) and breast-obsessed producer (Craig Robinson) assembles at the coffee house where Zack works to throw together the masterpiece in record time.

The film is a riot, with a surprising yet welcome tenderness and honesty underlying some hilarious gross-out moments involving constipation and a hand-warming pad.

The lovable Rogen and Banks are ably supported by a strong ensemble cast, including Justin Long in scene-stealing form as a bona fide adult film star who tells his closeted partner (Brandon Routh): “I will be your sherpa up the mountain of gayness.”

The dialogue is littered with profanities, eliciting a guilty chuckle and occasionally a groan of disgust.

The ending is obvious from the opening frames but the fun comes from trying to work out how Smith will contrive his happy-ever-after, and more importantly, what bodily fluids might be spilt in the process.