Two episodes of an ITV sketch series starring comedy legends John Cleese, Tim Brooke-Taylor, Marty Feldman and Graham Chapman have been found after 47 years.

The British Film Institute has said that the two episodes of At Last the 1948 Show – a sketch comedy with spoofs of different broadcasting formats - have been discovered in the archive of the late journalist Sir David Frost and will be shown for the first time since they were aired on ITV in 1967.

The discovery is being dubbed a major find for fans of the early flowering of surreal British television comedy which led to the creation of the Monty Python programmes two years after the series aired. At Last the 1948 show is famous for containing the first use of the phrase "And now for something completely different" which became a Python catchphrase and for showcasing the first outing of the Four Yorkshiremen sketch.

The two new finds will also be presented at the BFI’s cinema in December as part of the Institute’s annual celebration of newly recovered television programmes, Missing Believed Wiped.

The find was made by Missing Believed Wiped co-ordinator Dick Fiddy when he was invited by family members to explore the collections of the late Sir David Frost who was executive producer on the show.

The programmes were contained on two reels of 16mm film and have not been seen since their original broadcast in 1967.

Rediscoveries from various sources mean that today, of the thirteen episodes of the show which were produced, a total of more than nine episodes worth of material is now contained in the BFI National Collection of Film and Television.

Fiddy, the BFI’s Television Consultant said: “This latest recovery is a crucial find. It represents a key moment in the history of British television comedy featuring the combined talents of some of its greatest exponents. These gifted comedians, all in their 20s and 30s, were let off the leash and allowed to experiment with style and content, resulting in shows which have had an enduring influence on comedy worldwide.

“Even very recently the famous ‘Four Yorkshiremen’ sketch - which originated on At Last the 1948 Show - was used as the opener for the Python’s stage shows at the 02 and had been performed previously by the team in galas such as the Secret Policeman’s Ball.”