To be honest, I was very doubtful about whether I was going to enjoy Fat Pig. Neil LaBute’s take-no-prisoners style isn’t generally my cup of tea, and, as a lady on the large side myself (I’m not as squeamish about the euphemisms as the play’s characters), I wasn’t sure how I’d take to the show. But the lure of some of my favourite TV actors was too strong.

On arriving, I was amused to see a large number of well-upholstered ladies in the audience – although it did make me worried for the cast’s safety as the Trafalgar Studios aren’t very big (actually, that’s a sore point. Twice now, we’ve had seats that tip alarmingly unless you sit just so, rigid throughout the performance, and even my slim friend ended up virtually sitting on the knee of the man next to her, there was so little room). I was also heartened to get a glimpse of the writer/director rushing up the stairs just as we came in and he’s no skinny minnie himself…

The play centres on Tom, a basically sweet guy, who meets and falls in love with Helen. His co-workers and supposed friends, Carter and Jeannie (the latter of whom dated Tom) want to know who his new love is and disapprove of her size. Will Tom have the courage to go with what makes him happy or will he follow the crowd?

The answers are never simple, especially as Jeannie is presented as a stereotypical Manhattanite ball-breaker, whereas Helen is warm, funny, gorgeous and the only one of the four who seems to have any kind of personality. Carter is ashamed of the way he treated his overweight mother when he was a child, but is unrepentant about his hostility to Helen.

The result is surprisingly touching in place and uncomfortably funny in others (often the audience isn’t sure if it’s laughing at the characters or at itself). Sadly, it’s slighter than its svelte characters and doesn’t really come to an end – it could be argued that life doesn’t, but I’m paying to see a drama not a documentary.

Both Robert Webb and Kris Marshall bring their familiar TV personas to play on Tom and Carter. The former brings a great deal of charm to the nerdy Tom and isn’t afraid to make a joke at his own expense. The latter’s rangy frame and shark grin are ideally suited to the boorish Carter, and he manages to keep the audience’s sympathy despite being shallow and vile – a hard trick to pull off. Joanna Page is less assured as Jeannie – the part’s bitchiness is not an ideal fit for her – but she’s stronger when Jeannie really lets rip at a vacillating Tom.

All three would have been better served had the play’s location been transferred to London (there isn’t really anything in the play that would prevent this as the characters are as familiar here as they are in the US) and they’d been allowed to do it in their own voices – at times, they seem to be concentrating more on hitting the American accent than on their performance. We did go during the previews, so the accents may settle in over time.

The revelation of the play is, however, the wonderful Ella Smith. Her Helen is heartbreakingly warm and sweet and she’s absolutely luminous (and the accent’s dead on). It’s easy to see why Tom would chose her over Jeannie, but equally easy to see why she needed a stronger man. It’ll be the more familiar names that will pull the crowds in, but it’ll be Ella they rave about afterwards.

Fat Pig, Traflagar Studios, Whitehall, London Until Sep 6. Box office: 0870 060 6632