In these days of financial uncertainty for the West End, theatregoers all too often seem to be faced with insipid imports (such as The Drowsy Chaperone), rehashes of popular material (shows such as Daddy Cool) or the stunt casting of American film stars and soap/reality ‘celebrities’ (in shows such as Chicago). And many of the productions that are brought into town for a run are less than appetising, less alone challenging.

Happily, there is an exception to all of this in the form of Elling, starting a run at the Trafalgar Studios following its sellout run at the Bush Theatre. Even if it were not of such high quality, it would be successful?its star, John Simm (last seen biting the furniture in Dr Who and embracing the 1970s in Life on Mars), brings a ready-made audience.

But it doesn’t need it. The script (adapted from Ingvar Ambjornsen’s cult novels by Simon Bent) is both witty and affecting?we’ve been quoting it ever since (for example, ‘I can’t lose my mind again; I’d go mad’ and ‘Mother did the shopping; I did the ideology’). The performances of the two stars as the odd couple Elling and Kjell Bjarne (Simm and Adrian Bower) add extra depth and emotion to the proceedings. They’re assisted by an appealing supporting cast of Ingrid Lacey, Keir Charles and Jonathan Cecil.

Elling and Kjell Bjarne (he’s invariably known by both names) meet in the asylum and become fast friends despite self-confessed mummy’s boy Elling’s tightly wound anxiety and Kjell Bjarne being ‘an orang-utan’ to quote Elling, obsessed with food and sex (which he’s never had). While Elling is neurotic, Kjell Bjarne is what used to be described as simple. When the two are released from the institution to live in a flat in Oslo, we follow their attempts to cope with the real world.

Put simply, the plot may sound off-putting, but don’t be fooled?what would, set in England, be an exploration of social service failure and an indictment of care in the community, is, set in Norway, innocent and charming. Bower brings a great deal of charm to what could have been a one-note part and Simm is simply wonderful, his body twisted up tense as a spring, nostrils flaring in Kenneth Williams-style disapproval.

You won’t regret getting your ticket.

Trafalgar Studios: 0870 060 6632; www.theambassadors.com.