Two long-lost short films starring Peter Sellers will be shown in public for the first time in 2014, more than half a century after they were made.

In 1957, the iconic comic actor starred in the 30-minute shorts, Dearth of a Salesman and Insomnia Is Good for You, for the now-defunct Park Lane Films. They were discovered in 1996 in a skip outside the production company's headquarters by the building manager, Robert Farrow, who says he "put them in a cupboard and pretty much forgot about them".

He continued: "During a recent clear-out, I found them … and decided to see what the tins contained. It was then I realised they were two Sellers films, including the negatives, titles, show prints, outtakes and the master print. It was amazing."

The shorts were made early in Sellers's career, after success on radio with The Goon Show but before his work on screen took off. He went on to find global fame with the Pink Panther films and Dr Strangelove.

Farrow gave the shorts to Paul Cotgrove, director of the Southend-on-Sea film festival, who will screen them next May on the event's opening night, after both have been digitally restored. Little is known about the works, which were deemed lost for good, but both were co-written by the Canadian novelist Mordecai Richler. Sellers plays multiple roles in each film, making them a cross between a sitcom and sketch show.

Cotgrove told the BBC: "They're a kind of a pastiche of the public information films at the time. They're not riotous comedy, they're just good fun to look at."