5 February 2016 Last updated at 13:10 GMT
It shows cast members, including Arthur Lowe, John Le Mesurier and Clive Dunn interviewed in character as they attended a vintage vehicle rally in Brighton in 1974.
The BBC South Today film report, which has not been broadcast for more than 40 years, was found in the library at BBC Broadcasting House in Southampton.
A film version of the legendary TV sitcom, directed by Oliver Parker and staring Toby Jones and Catherine Zeta Jones has been released.
News footage of the original cast of Dad's Army being interviewed has been unearthed.