The police investigation could force a delay to the internal inquiry commissioned by Johnson. | POOL

British police said on Tuesday they had opened an investigation into possible COVID lockdown breaches at Prime Minister Boris Johnson's Downing Street residence after receiving evidence from an internal government probe into a series of gatherings.

Johnson is fighting for his political life after a series of claims that he and staff partied at the heart of the British state in breach of the rules they had themselves imposed to fight the COVID-19 pandemic.

Revelations of revelry, including boozy parties in Downing Street, suitcases of supermarket wine, a broken children's swing, a wine fridge and jokes by staff about how to present such parties to reporters, have hammered Johnson's ratings.

ITV reported on Monday that Johnson had attended a surprise party on his birthday in 2020. Up to 30 people attended the event in the Cabinet Room of No. 10 Downing Street, his office and residence, the broadcaster said.

After initially refusing to investigate the gatherings at Downing Street, Britain's top police officer, Metropolitan Police chief Cressida Dick, said on Tuesday that an investigation had been opened.

"I can confirm that the Met (Metropolitan Police) is now investigating a number of events that took place at Downing Street and Whitehall in the last two years in relation to potential breaches of COVID-19 regulations," she said.

The Cabinet Office said its own investigation, being carried out by senior official Sue Gray, was continuing and there was ongoing contact with the police. It was unclear when the results of that probe will be published. It might be delayed.

Revelations about the gatherings have prompted some of Johnson's own Conservative Party lawmakers to call for him to resign, though so far fewer than the 54 required to trigger a confidence vote that could result in a leadership contest.

Johnson's future

Johnson has survived scandals throughout his career but his premiership, straddling both Brexit and the worst pandemic for a century, has been defined by turbulence, including his own battle with COVID-19.

His 2019 plan to suspend parliament and force Brexit through was overturned by the Supreme Court before, to the delight of millions who changed their political allegiance to vote for him, he eventually negotiated a deal for Britain's EU exit.

Months later when the novel coronavirus struck he delayed shutting the country down longer than his international peers, a decision that was sharply criticised as COVID-19 deaths rose to over 150,000, the seventh-highest among countries.

Johnson nearly died from the disease himself before recovering to lead a world-leading vaccine rollout.

But reports that he and his own Downing Street staff were flouting the rules they imposed on the British public are testing Johnson's legendary ability to survive.

"I'll be honest I always voted for Boris but he's got to go doesn't he? You break the rules, you've got to go," said Ian Dowrich, a 59-year old builder from Brentwood, Essex.

According to ITV, Johnson attended a surprise birthday party in Downing Street on June 19, 2020, when social gatherings indoors were banned. He was presented with a cake while his partner Carrie led staff in a chorus of "Happy Birthday". His office said Johnson attended for less than 10 minutes.

Met chief Dick said police had not typically investigated every alleged lockdown breach but she felt there were grounds to do so now after receiving some findings from Gray's inquiry.

She said police had looked at several factors when deciding whether to investigate any reported lockdown breaches, including if "there was evidence that those involved knew or ought to have known that what they were doing was an offence".

Deputy Leader of the Labour Party Angela Rayner welcomed the investigation and renewed opposition calls for Johnson to resign.

"Boris Johnson is a national distraction. Conservative MPs