Being in a theatre production is always a voyage of discovery because you learn more and more about the play and the characters. But the BBC3 documentary Growing Up Down's also shows the actors discovering a great deal about themselves. And we discover a lot about them too.

I think the BBC were wrong to call tonight's documentary about the Winchester theatre group Blue Apple 'Growing Up Down's'. It sounds like a film about children or at the very least reinforces a mistaken view that adults with a learning disability are like children. The fact is, the documentary is about a group of adult actors with various learning disabilities of which Down's Syndrome is one.

What is fascinating about it and why I encourage you to watch it is that it is about them putting on a production of Shakespeare's Hamlet. There are tears and laughter as they struggle to come to terms with its tragic themes and the feelings it brings out in them.

People with a learning disability may lack confidence or sometimes an understanding of the world. Taking part in drama helps them gain both. It helps them make friendships and to work in collaboration. Blue Apple Theatre, of which I am Chair of the trustees, runs drama and dance workshops for people with a learning disability. Just as importantly, their public shows put at centre stage, literally, people who are marginalised in society.

The people in the documentary are a little different from the other participants in that they are a core of actors within Blue Apple who are or have aspirations to be professional actors. Made by Will Jessop, it tells the story of a professional touring production by them. This is their opportunity to do some serious acting. It is also a showcase for people who could be cast in film, TV or stage productions but so often aren't out of pure (albeit subconscious) prejudice.

It used to be- and possibly still is- the case that black actors were overlooked for parts which they could easily play. Only recently have black British actors like Idris Elba or Adrian Lester managed to get lead roles. I saw Lester as a brilliant Othello at the National Theatre last year but amazingly it was only in 1999 that a British black actor finally played the role. It wasn't that many years ago that there were no black families in Coronation Street.

I can remember a pantomime producer telling me that he didn't like casting black actors because there weren't black people around in the days of Dick Whittington and Cinderella. Even if this were historically true, which it isn't, since when has panto been the acme of authenticity? There is still controversy over the casting of a mixed race actor as one of the BBC's Musketeers, even though the author of The Three Musketeers, Alexandre Dumas, had a black father.

I believe actors with disabilities are in the situation that black actors were in pre-21st century- invisible, even though they are everywhere. In situations where there is absolutely no reason why a part shouldn't be played by someone with a disability, many producers and directors simply don't think about casting anyone other than their idea of 'normal'.

The London Paralympics did a great deal to change our view of people with a physical disability. Blue Apple is trying to do the same in its small way for people with a learning disability. I hope the documentary will help everyone who sees it realise that the people taking part are human beings and not a label called 'learning disability'. We need, as Hamlet puts it in his famous soliloquy, 'to take arms against a sea of troubles and by opposing, end them.'

When I saw Blue Apple's Hamlet, I was moved and excited by the acting. Tommy Jessop as Hamlet is particularly good at engaging the audience and making the words seem like the thoughts have just come to him. The production revealed to me aspects of the play I had not appreciated before. Whenever I visit the theatre, I hope to get this from the actors. The fact that these actors had learning disabilities was only relevant to the extent that their view of life cast a new and interesting light on the play. They have an openness and lack of guile that exposes the heart of the emotional content.

Our greatest poet and playwright understood that acting has this power to raise both performers and audience above what we are to what we can be. No-one could have put it more apositely or more poignantly than Shakespeare when, towards the end of the film, Tommy as Hamlet says, 'Look through our sad performance and see that we fools of nature are wondrous too.'

Growing Up Down's is on BBC3 on Wednesday 5th February at 8pm and available on BBC iPlayer for seven days after.

This blog was written by Paul Lewis, owner of the marketing consultancy The Lewis Experience and online retailer Your Life Your Style, and former Head of Marketing at The Mayflower Theatre. You can connect with him on Google+ and LinkedIn.