The moment quickly went viral, with thousands seeing it live and many more watching it online as videos spread across the internet.
Users described the gaffe as "a moment of light relief" and others milked it for a bit of comedy.
Boris Johnson is battling to remain in office, shrugging off calls for his resignation after a slew of officials resigned from his government. A total of 42 MPs have now quit their roles, the Guardian reports.
Johnson rejected demands that he step down during a stormy session of the House of Commons in the wake of a furore over his handling of sexual misconduct allegations against a senior official.
Later in the day, a delegation of some of his most trusted allies in the Cabinet paid a visit to Johnson at Downing Street to urge him to go, Britain's Press Association reported. Senior minister Michael Gove was sacked for his role in the standoff.
Johnson rejected the group's suggestion he seek a "dignified exit" and opted instead to fight for his political future, citing "hugely important issues facing the country", according to the news agency. The prime minister told his colleagues there would be "chaos" if he quit, possibly leading to an early election and "almost certain" defeat for the party.
- Additional reporting, AP