The BBC Television and Radio archives are among the largest collections of broadcast material in the world. The radio material dates back to 1924, and the television archive holdings begin in November 1936.
There are more than 300,000 hours of radio material and 600,000 hours of television material held in the BBC archives.
These vast collections are growing on a daily rate as material from five national radio networks, five television channels and local radio stations pour into the archive each day.
Last year the BBC launched a programme to digitise the television and radio archives. The first priorities were the transfer to digital formats of Radio 1 live sessions and television programmes held on two inch video tape - mainly studio-based entertainment shows and sport. The BBC has earmarked a further £20 million over the next three years for the project.
It is estimated a total of £60 million and ten years will be needed to preserve every part of the archive.
1 May, 8pm
(BBC broadcast 10 May)