Boris Johnson has insisted he “broke no rules” after being pictured hosting a quiz night in Number 10, as Tory MPs said on Monday night that the Cabinet Secretary must be given time to conduct a “thorough” investigation.

On Monday, Mr Johnson hit back at allegations that he may have misled Parliament and broken Covid rules as he continued to face questions over his participation in events in Downing Street last Christmas.

He also confirmed that Simon Case, the head of the civil service, would expand the scope of his investigation to include the quiz night, which took place on Dec 15 last year.

It follows the unearthing of an image of Mr Johnson this weekend, which appeared to confirm he had taken part in the quiz three days before the alleged Christmas party in Downing Street.

The picture, obtained by the Sunday Mirror, showed him sitting in front of a laptop in the Number 10 library alongside two colleagues, wearing tinsel and a Christmas hat.

Number 10 has insisted the event was held virtually and that Mr Johnson joined “briefly” to “thank staff for their hard work throughout the year”. A spokesman also said staff who participated from Whitehall did so from their desks.

However, sources have suggested several staff participated by gathering around screens in the building, while Sir Keir Starmer, the Labour leader, suggested Mr Johnson’s actions appeared to breach Covid rules.

London was under Tier Two restrictions at the time the event took place, with no mixing of households indoors allowed other than support bubbles, while work lunches or parties deemed a “primarily social activity” were also prohibited.

Asked about the controversy while on a visit to a vaccination clinic near Paddington, west London, Mr Johnson said: “I can tell you that I certainly broke no rules – the whole thing will be looked into by the Cabinet Secretary and what I’m focused on, frankly, is the vaccine rollout.”

Asked whether that meant Mr Case’s investigation would include the quiz, Mr Johnson said: “He’s looking at all these things. Is that the thing with the Zoom call? Yeah.”

It means that Mr Case’s investigation will now cover four events – an alleged leaving do for a senior Number 10 aide on Nov 27, a gathering in the Department for Education on Dec 10, a Christmas quiz in Number 10 on Dec 15, and a party on Dec 18.