The BBC has claimed it made a “mistake” in editing a clip where it cut out an audience laughing at Boris Johnson, insisting the decision was made due to time constraints rather than political bias.

In the Question Time leaders’ debate special, broadcast on BBC One on Friday night, an audience member asked the prime minister: “How important is it for someone in your position of power to always tell the truth?”

Her question to Johnson was met with laughter, followed by applause, with Johnson struggling to reply. But in the version shown on the following day’s lunchtime news bulletin the laughter had been removed, with the BBC initially saying the edit had been made for time reasons before it rowed back and admitted its error.

In a sign of the changing power dynamics between the BBC and its viewers during this election, viral online videos claiming to highlight aspects of BBC bias are increasingly reaching larger audiences than the original programmes.

The original Weekend News bulletin attracted just 1.6m viewers across both BBC One and the BBC news channel on Saturday, fewer than the number who have watched Facebook and Twitter clips highlighting the BBC’s decision to edit out the laughter.

Although social media views are calculated using a different methodology to television ratings, it is highly likely that substantially more people have seen coverage of the controversial edit than ever saw the original news bulletin – especially when combined with widespread news coverage of the edited footage.

The discrepancy was spotted by Nick Flaks, a resident of Brighton, while watching the lunchtime news: “I rewatched both clips, and found the editing department had cut about 1.5 seconds of laughing on the topic of trust and instead gave the appearance that Johnson was being clapped at, cheered and supported by the audience instead of being ridiculed.”

Flaks, however, quickly located the original Question Time footage using the BBC’s iPlayer catch-up service and produced a short clip using his iPad’s video editing software and uploaded it to Twitter. This prompted accusations against the BBC from the writer Peter Oborne that this “kind of thing was normal on state TV in Soviet Russia” and a defence from BBC presenter Huw Edwards that this was an error rather than a conspiracy.

Flaks said the whole thing could have been avoided if the BBC had not made the edit: “I wholeheartedly support the BBC and the idea of public broadcasting in general. However, I think that in recent years, particularly the news/politics department have sacrificed accuracy on the altar of ‘impartiality’. It’s important for the public to know that a room full of people laughed at our prime minister especially as the question was about truth and trust.”

He added: “I slightly regret that the post has fed conspiracy theories about the BBC but in a way they’ve only got themselves to blame.”

During this election campaign the BBC has already had to apologise for erroneously using archive footage of Johnson laying a wreath at the cenotaph on BBC Breakfast, while some of the most viral videos of the campaign have involved claims that the broadcaster is trying to keep the truth from the public.

After Flaks’ video went viral, the Liberal Democrats wrote to media regulator Ofcom to complain about the BBC’s decision to remove the laughter from the lunchtime bulletin. This is despite Ofcom rules clearly stating that all complaints must be addressed by the BBC in the first instance.

The footage – complete with laughter – was broadcast in full on the original Question Time special, which attracted 4.3 million viewers – and the Friday evening News at Ten, which pulled in an audience of 3.2 million.

A BBC spokesperson said: “This clip from the BBC’s Question Time special, which was played in full on the News at Ten on Friday evening and on other outlets, was shortened for timing reasons on Saturday’s lunchtime bulletin, to edit out a repetitious phrase from Boris Johnson.

“However, in doing so we also edited out laughter from the audience. Although there was absolutely no intention to mislead, we accept that this was a mistake on our part, as it didn’t reflect the full reaction to Boris Johnson’s answer. We did not alter the soundtrack or image in any way apart from this edit, contrary to some claims on social media.”