If anyone epitomises the BBC's traditional values and integrity, it's David Attenborough.

However, a previously unseen letter has been unearthed that shows how things could have been very different for Sir David, 99.

The correspondence, from July 1952, reveals the haphazard way in which his seven-decade career at the corporation began.

As a budding naturalist, a young Sir David had applied to become a producer.

The BBC turned him down, but then encouraged him to apply for its television training scheme, which prompted him to give it another shot. 

The letter tells the then 26-year-old that his interview was successful, adding: 'I am now writing to let you know that you were selected for the Television Training Course as Talks Producer.'

The BBC said yesterday that the success of his second application 'arguably changed the course of broadcasting history'. 

Sir David rose to become controller of BBC Two and director of programming during the 1960s and 1970s before presenting scores of award-winning documentaries about the natural world.

His letter from the BBC and his earlier application for the TV training scheme will now form part of a new archive of more than 50,000 documents that detail different aspects of the 100-year-old national broadcaster's history.

The BBC said it will would be made available to researchers and the public, 'shining a light on the BBC's role in cultural and social history'.

In another letter, aspiring actress Vanessa Redgrave, 15, asks executives to give her and her brother Corin an audition. She eventually won an Oscar and her brother became one of the finest Shakespearean actors of his generation.

The archive also details the 'untold story' of how the BBC tried to get Sir Laurence Olivier to make his TV debut in 1949. 

BBC executive Cecil Madden told Olivier's producer, Anthony Bushell: 'Try to persuade Olivier to do some television for us. We would put on almost anything he liked.'

Olivier, however, never starred in a BBC drama.

Noreen Adams, BBC director of Archives Technology and Services, said: 'This release is part of our plans to make more of the BBC's written archives available to the public. This first batch includes extraordinary material.'