It was a show that gave a voice to groups on the fringes of society, from transgender women to those totally opposed to immigration. 

Open Door was the brainchild of Sir David Attenborough, before his wildlife programmes made him a national treasure. 

In his role as the BBC's director of programmes, Sir David proposed the radical show in December 1972, and it aired for a decade from April the following year.

Speaking tonight in his BBC series Story of Us, historian Sir Simon Schama says: 'It was really a kind of mini cultural revolution. The slogan of Open Door, "Your Own Say... In Your Own Way", says it all. 

'It turned what broadcasting was, what it meant to everybody, completely upside down.'

Those who made shows were allowed to control the direction of an entire episode, largely free from interference by the BBC.

Groups given screen time included transgender women calling themselves the Transex Liberation Group, black teachers and housewives campaigning under the banner of 'Wages for Housework'.

In his five-page proposal for the show, which only became public decades later, Sir David told the BBC board: 'It should not be proposed that these programmes would be made exclusively by the lunatic fringe, nor that they would form an unbroken series of vociferous radical manifestos.

'Some may not put arguments of any kind but simply provide entertainment - new music; odd minority sports; documentary insights into community activities.'

However, the show in February 1976 that gave a platform to 'The British Campaign to Stop Immigration' generated controversy, with the group using openly racist language.

When the episode was due for its Saturday repeat days after first airing, critics argued that it should not be shown again.

There were fears that the show incited racial hatred, but the BBC insisted on upholding freedom of expression and so it went ahead.

In the programme given over to the Transex Liberation Group, in June 1973, the presenter says: 'Of the four of us in the studio this evening, two are transsexuals awaiting sexual conversion surgery, and the other two, including myself, are what as known as sex changers.

'Woman born of man.'

One transgender woman who had not yet had gender reassignment surgery then spoke of their experience.

They said: 'It's like living on the edge of a volcano. 

'Because, if anything happened to me, if I got knocked down by a bus or a car, or anything, or taken ill, and I was put into hospital, and they found out I was still biologically male, I would be put into a men's ward, which would be so embarrassing... or if I wasn't put in a men's ward I would be put in a sort of side ward, and made to feel an oddity, whereas I feel I'm not an oddity.' 

The Vegan Society were given their own show in January 1976. One campaigner said in the programme: 'Ever since I started a vegan diet, trying this and trying that, my health has steadily improved.'

In February 1976, women campaigning to be paid for housework made a programme called 'All Work and No Pay'.

The narrator says: 'Housework, the work all women do. The only work that isn't considered work.

'The only work you don't retire from. The only work you don't get wages for.' 

The show also tackled difficult subjects such as domestic abuse and racial disparities head-on. 

In an edition called 'Battered Wives', which aired in October 1973, one abuse victim said: 'I think that a lot of husbands wouldn't batter their wives if they realised that their wives could get up and walk out. 

'A lot of men in our refuge have said to their wives, "oh you can't leave, there's nowhere for you to go."'

In April 1973, the month the programme debuted, an edition profiled black teachers. 

Presenter Mike Phillips opened by saying: 'We are a group of black teachers and we made this programme about the poor level of achievement of black children in the English school system. 

'That's the problem that is worrying most of our black parents out there at this moment.' 

He added: 'So if you're a black parent and you are sitting there thinking that just because you dress up your child neat and tidy and send him to school in the morning, he is going to come out as a civil engineer, or a lawyer, or doctor, or even as an average skilled man, think again.

'Because the most likely thing is that he will turn out, not to do better than you, but to do the same or worse, because that is the position that society has marked down for him.' 

Sir David had admitted in his proposal that 'the danger of programmes being dull is real', and there were many editions that were not entertaining viewing.

But, in highlighting why Open Door was radical, Sir Simon adds: 'You had vegans, anarchists, feminists, anti-feminists, anti-racists, anti-immigrants, transsexuals, sci-fi UFO enthusiasts.

'Every single bit of organised, clubby, crusading, campaigning passion had a chance to be on air.

'A lot of the issues are goodness knows still with us today. They were not trivial. 

'At some point, in nearly all the programmes, they make really important statements that make us pause.'

Simon Schama's Story of Us airs on BBC Two at 9pm.