THE Switch may have Jennifer Aniston as top billing on all the marketing, but it’s not really her film.

It actually belongs to her male co-star Jason Bateman who steals the show as her neurotic best friend.

Kassie (Aniston) is rapidly approaching 40 and her biological clock is ticking. With no male prospects on the horizon and desperate to conceive, she decides to use a sperm donor much to the objection of Wally (Jason Bateman).

Not wanting to have a completely anonymous donor, she pays the seemingly perfect Roland (Patrick Wilson) for his sperm.

But when her friend Debbie (Juliette Lewis) throws her a “getting pregnant” party, Wally gets drunk, accidentally spills Roland’s sample and decides to swap it for his own.

After getting pregnant, Kassie moves away. Wally can’t remember anything about the evening but realisation and memory begin to dawn when Kassie returns to New York seven years later with her son(Thomas Robinson) who happens to share more than a few characteristics with his unsuspecting father – hypochondria, neurosis and a nagging feeling that he just doesn’t fit into the world.

The film unexpectedly centres on the touching relationship between father and son – their banter is witty and sharp and displays a frequently funny take on some of life’s absurdities.

It’s surprisingly touching and strikes an unusually authentic tone in a movie expected to be a hapless rom-com.

Unfortunately, the same can’t be said for Jennifer Aniston and supposed-father Patrick Wilson who are relegated to background characters, mere clockwork automatons going through the motions.

It’s simply impossible to care about their relationship which is so obviously mismatched and doomed from the outset.

Jeff Goldblum is a wonderful addition to the cast, playing Wally’s sardonic boss Leonard – with his trademark unforgettably fractured delivery, he’s a frequent highlight.

He also gets some of the best lines in the film - ”She wouldn’t know good sperm if it slapped her in the face.”

Sadly he’s rather underused and as a result the film is short on laughs, playing out more as a romantic drama than a comedy.

It’s all a fairly enjoyable ride until the final act when things start to rapidly unravel.

The relationship between Kassie and Roland accelerates out of all proportion – suddenly they’re moving in together and Roland’s on the verge of proposing.

It’s all so unlikely, that it’s a clear sign for Wally to come clean about his misdemeanour all those years ago.

The Switch is a surprisingly entertaining romantic drama but suffers from an uneven tone and a desperation to trade off Jennifer Aniston’s star pulling power.

It’s the scenes with Bateman and Robinson which are the real highlights, elevating the film above what is a frankly ridiculous premise and beyond Aniston’s two-dimensionality.

The Switch (12A) is out today.