Directed by Jonny Campbell, starring Anthony McPartlin, Declan Donnelly, Bill Pullman, Jimmy Carr, Harry Dean Stanton, Orson Bean, Madeleine Moffat, John Cater and Omid Djalili.

Jonny Campbell, director of TV's 'Shameless', may have had brief reservations about the casting of two Geordie lads with very well-known mugs in the lead roles of this quirky, other-worldly romp. But sometimes risks pay off.

McPartlin and Donnelly - aka Ant and Dec - play two hapless chancers (well, essentially Ant and Dec) in this gimmicky sci-fi/comedy, which explores the true story of Ray Santilli and his best friend Gary Shoefield, who happen upon some rare footage that may prove the existence of aliens.

Ray (Donnelly), being the scatty one, runs a market stall selling pirate video tapes that he records at his Nan's house. Gary (McPartlin), being the more sensible one, works as an accountant in the legal department of a biscuit company. Little do they know that a US shopping trip to buy Elvis memorabilia for Ray's stall could change their lives forever.

During the trip Ray meets a cameraman, Harvey (Stanton), who wants to sell him some footage of Elvis. It's impressive, but not nearly as impressive as what comes next. After driving Ray out to his home, in the middle of nowhere, Harvey produces the most amazing piece of film that Ray will ever see, possibly the most amazing piece of film the world will ever clap eyes on. The grainy footage appears to show an alien autopsy at a disused army base in Roswell, New Mexico, back in 1947. And, as luck would have it, the old man is eager to sell the tape, naming his price of £30,000 - the kind of money Ray and Gary have never even dreamed of seeing.

Enter loan shark, drug dealer and crop circle fanatic Voros (Otto), a man with money to burn and some pretty crazy fantasies. And when Ray tells him about his amazing discovery he's naturally eager enough to come on board. So, with their new-found financial backing, the boys collect the tape, take it home to the UK and set about making a name for themselves. But disaster is never far away for the duo and when the film becomes exposed to light it begins to disintegrate, destroying the precious footage.

There's only one thing for it. The pair must make a replica film if they are to convince the world of what they saw and, more importantly, cash in. At this point they enlist some partners in crime – Ray's Nan (Moffat), Nan's boyfriend (Cater), local butcher Melik (Djalili) and a few groupies for good measure. The end result is a mannequin autopsy in Gary's sister's front room, which must be passed off to the world as a genuine alien autopsy from the 1940s, a feat that is surprisingly easily achieved by the lads.

Several foreign chat shows and a few scary encounters with loan shark Voros later, the boys are in danger of being exposed. The CIA is involved, and there are suddenly spies on street corners and between the bed sheets. Ray and Gary are treading on very thin ice, with little more than their charm to keep them afloat.

McPartlin and Donnelly obviously have a very comfortable working relationship and appear totally at ease in each other's company on screen, hitting the right notes chemistry-wise. There are also impressive cameos from Bill Pullman (as the film director who wants to make a documentary about the lads), Harry Dean Stanton (as the military cameraman who sells them the tape) and comedian Jimmy Carr (as Gary's uptight, pretentious boss).

'Alien Autopsy' is daft fun. It's lively. It's entertaining and it's fairly original. Everyone benefits here from the fact that there's inevitably something likeable about the story of underdogs who spot an opportunity and grab the chance (regardless of how crazy the story is).

Credit to Ant and Dec - at least brave enough to leave their TV comfort zone - on a big screen debut that might surprise a lot of their critics.

Linda McGee