Having checked a bit more I find the film Elling is based on, is itself based on the Norwegian play of the book Brødre i blodet (Blood Brothers) by Ingvar Ambjørnsen. (And I hope the Norwegian characters appear correctly!) It's the story of a pair of roommates from a psychiatric institute who are given the chance to move to an appartment and live in the community.
John Simm and Adrian Bower were excellent as the two main leads, and believable as two different characters who yet have a strong friendship. It is a warm amusing play, with several lines which throw common situations in life into a new light. There are moments of sadness and poignancy as they meet difficulties in coping with the outside world and new relationships. Their social worker is no saint, and definitely seems to be of the school of 'tough love', but his frustration at their lack of progress and his surprised delight when they do achieve something acts as a good contrast to the general feel-good aspect of the play.
The play only has five actors, with the two younger ones handling several parts with aplomb. I think they particularly enjoyed their stints as modern performance poets. (Ingrid Lacey was Helen in 'Drop the Dead Donkey', and I can't find anything that Keir Charles has been in that I remember watching, but he has a familiar face.)
The other actor who plays a distinguished but retired poet, Jonathan Cecil, is one of those character actors that always seems familiar even though you can't remember what specifically you've seen him in, this is the only picture I can find quickly of him.