Boris Johnson is to face a Commons vote over whether he misled parliament over partygate.
In a major blow for the prime minister, Speaker Lindsay Hoyle approved a Labour attempt to call in the privileges committee to launch an investigation into his behaviour.
It means MPs will hold a debate on Thursday on whether Johnson misled them when he claimed in December that Covid rules were followed at all times in Number 10.
They will then get a vote on whether to refer the matter to the privileges committee.
Johnson has been accused of lying after the Metropolitan Police issued more than 50 fixed penalty notices over lockdown-busting parties in Whitehall and Downing Street.
That included £50 fines for Johnson himself, his wife Carrie and chancellor Rishi Sunak.
The seven-strong, cross-party privileges committee has a Conservative majority but is chaired by Labour MP Chris Bryant.
The committee will be able to order the production of evidence, such as photos of gatherings in Number 10, as part of its inquiry.
It has the power to find an MP in contempt of parliament, with sanctions ranging from ordering an apology to expelling a member from the house.
Hoyle told MPs: “It is not for me to police the ministerial code, I have no jurisdiction over the ministerial code even though a lot of people seem to think I have. It is not the case.
“Secondly, it is not for me to determine whether or not the Prime Minister has committed a contempt. My role is to decide whether there is an arguable case to be examined.
“Having considered the issue, having taken advice from the clerks of the House, I’ve decided that this is a matter that I should allow the precedence accorded to the issue of privilege.
“Therefore, (Sir Keir Starmer) may table a motion for debate on Thursday.”
Hoyle announced his decision shortly before the PM makes a Commons statement in which he is expected to apologise for breaking his own Covid laws, but insist he has no intention of resigning.
Given the Conservatives’ healthy Commons majority, it is highly unlikely that Johnson will lose Thursday’s vote.
However, it forces Tory MPs - many of whom are furious at the PM’s behaviour and expect further fines to be issued by the Met - to decide whether they want to publicly show their support for him.
A Labour source said: “Any Conservative MP considering voting to block this investigation would be voting for a cover up. They should reflect on the mess they got themselves into over Owen Paterson before falling into line.”
Lib Dem leader Ed Davey said: “The British public have declared Boris Johnson a liar. Now it’s time for Parliament to do the same.
“The country cannot afford a Prime Minister who breaks the law and lies about it, especially when families are facing a cost-of-living crisis.
“Johnson has taken the British people for fools for far too long, and it’s time for Conservative MPs to show where they stand. They must do their patriotic duty and kick Boris Johnson out of Downing Street once and for all.”