Back in 1969, a BBC documentary aired that offered a tantalising glimpse into the inner workings of the lives of the Royal Family. It was so controversial that a staggering 30 million viewers tuned in to watch it. Yet while her subjects were delighted with the chance to peek behind the royal curtain – creating a new sense of proximity to a family traditionally kept at a careful distance – the Queen is believed to have regretted agreeing to the film, subsequently requesting that it never be broadcast again.

Now, however, the film has resurfaced and it was reportedly leaked on YouTube this month by an unknown user. It stayed on the platform for long enough for a few thousand viewers to watch the 110-minute programme, titled Royal Family. It’s not known how the user obtained the footage, which is believed to be protected under the copyright of the Crown.

The video was removed by YouTube on 28 January, having been brought to the attention of Buckingham Palace and the BBC, who submitted a copyright claim. A Palace source is quoted in the Times as stating: ‘It should not be on YouTube, and if it does appear, we would expect it to be taken down.’ A YouTube spokesman added: ‘This video has been removed due to a copyright claim. When a copyright claim is filed, we remove the content immediately, as is the case with this upload.’ The BBC reportedly declined to comment.

The film was compiled from 43 hours of footage filmed over the course of a year, which cost £150,000 at the time (around £2.5 million in today’s money). Something of a PR exercise devised by Sir William Heseltine, then the Queen’s press secretary, it was hoped that the documentary would present the royals in a humanising light – part of a plan by Heseltine to court public favour amid a bid for an increase of funding. It returned to public consciousness recently when the making of the film was fictionalised in Season 4 of The Crown.

The black-and-white film originally aired on the BBC in June 1969, before ITV broadcast a colour version a week on. Despite its success in ratings, a number of senior figures were concerned that it had compromised the sense of mystery and protection maintained by keeping the Royal Family at a distance. Sir David Attenborough, then a BBC controller, accused the documentary’s director Richard Cawston of ‘killing the monarchy’. Since 1972, the film has never been screened in full, although some clips of footage were used in the 2011 celebrations of the Queen’s Diamond Jubilee.

Princess Anne also expressed her misgivings about the documentary, once commenting: ‘I never liked the idea of the Royal Family film… I always thought it was a rotten idea. The attention that had been brought on one ever since one was a child, you just didn’t want anymore.’ Robert Lacey, however, a royal biographer and a historical consultant on The Crown, believes that the film did yield the intended result, noting: ‘The family got a new arrangement that updated their finances and kept abreast of the cost of living – something that has lasted ever since.’

In one moment from the documentary, the Queen, who was in her early forties at the time, likens the American ambassador to a gorilla. During conversation at a family meal, she states: ‘It’s extremely difficult sometimes to keep a straight face… The home secretary said to me, there’s a gorilla coming in. So I said, you know, what an extraordinary remark to make, very unkind about anybody. I stood in the middle of the room, pressed the bell and the doors opened… and there was the gorilla!’ While it’s not known when the encounter in question took place, the home secretary at the time the film was broadcast was James Callaghan. The recent US ambassadors to the United Kingdom were David KE Bruce and Walter Annenberg, who took over from Bruce in March 1969.

In another candid family moment, the Queen bought an ice cream for her youngest son, Prince Edward, from her own purse, adding: ‘This disgusting gooey mess is going to be in the car, isn’t it?’ Other memorable scenes include footage of Prince Charles waterskiing and the royals picnicking at Balmoral, with Prince Philip cooking sausages on a barbecue.