Two episodes of Doctor Who from the William Hartnell era, which have not been seen since 1965, have been released after being discovered in a private film collection.

The two episodes, released on Friday and starring Peter Purves as the Doctor’s companion, are parts one and three of a mostly lost 12-part adventure called The Daleks’ Master Plan, written by the Dalek creator Terry Nation and broadcast as part of the third series of Doctor Who in November 1965.

The two episodes – The Nightmare Begins and Devil’s Planet – were recovered by Film is Fabulous, a charitable trust run by film collectors with the aim of securing and preserving private collections. The estate of the deceased owner of the episodes, in whose collection the film prints were found, wishes that he remains anonymous, and so details about the circumstances of the find have been scarce.

Among his collection were four other Doctor Who episodes, but all of those were already held by the BBC. The original 16mm telerecordings of the two Dalek episodes have been restored, and were made available on iPlayer in the UK on Friday morning. They will also be shown at a sold-out event at Riverside Studios in Hammersmith, west London, Saturday afternoon.

The announcement that the episodes had been found was sprung as a surprise on Purves at a special private screening for him in mid-March. The actor, who would go on to be a Blue Peter presenter, plays the Doctor’s companion Stephen in the episodes. He was invited to a cinema in London under false pretences, and then shown the recovered programmes, which he described as “beautifully directed” by Douglas Camfield.

The episodes feature a significant milestone for Whovians, with the first appearance in the show of Nicholas Courtney, playing Bret Vyon. He would later go on to play Alistair Gordon Lethbridge-Stewart, who as the Brigadier of Unit was a regular foil for Jon Pertwee’s Doctor, and a character that appeared in stories with every Doctor from Patrick Troughton’s second to Sylvester McCoy’s seventh.

Ninety-five episodes of Doctor Who from the 1960s remain missing from the archives, after they were wiped or junked by the BBC during the 1970s. This was done to save space or reuse expensive videotape at a time when television was seen as an ephemeral product, and before the development of the home media market gave them any resale value. It is the first time episodes have been found since 2013, when nine Troughton-era episodes were discovered at a small TV facility in Jos, Nigeria, having been sold for syndication abroad.