Commons speaker Sir Lindsay Hoyle has told MPs to "sort out the mess we’re in" amid a furious political row over standards for MPs.
Opposition parties and campaigners have accused the government of corruption after an abandoned attempt to overhaul standards rules to protect former MP Owen Paterson from suspension.
Paterson announced his resignation last Thursday after the PM was forced into a U-turn over a decision to prevent his suspension for breaching lobbying rules by launching a review of the entire disciplinary system.
The speaker addressed the Commons at the start of an emergency debate on standards.
He said: “I granted this debate today because I thought it was essential to sort out the mess we’re in.
“We can start to do that today but it requires two things from us all.
"To tone down the party political sniping and focus calmly on making sure the system is effective as it can be.
"And for everyone to recognise if we’re going to achieve progress we’ll only do so on a cross-party basis.”
Watch: Boris Johnson refuses to apologise for handling of sleaze scandal
Cabinet Office minister Stephen Barclay opened the debate for the government by admitting it made a "mistake".
He told MPs: “I’d like, first and foremost, to express my regret and that of my ministerial colleagues over the mistake made last week.
“We recognise there are concerns across the House over the standards system and also the process by which possible breaches of the code of conduct are investigated.
“Yet whilst sincerely held concerns clearly warrant further attention, the manner in which the government approached last week’s debate conflated them with the response to an individual case.
“This House shares a collective interest in ensuring that the code of conduct reflects and fosters the highest standards of public life.
“The government fully recognises that the standards committee is critical to this, including the important role performed by its chairman (Labour MP Chris Bryant).”
Boris Johnson was accused of “running scared” after staying away from the emergency Commons debate.
Downing Street said the prime minister could not get back to Westminster in time following a long-planned visit to an NHS hospital trust in Northumberland.
Johnson also refused to apologise for the handling of the Paterson scandal.
He had supported Paterson’s allies’ attempt to review his sanction until opposition parties refused to take part in a Tory-led committee tasked with the review.
Many Tory MPs were angry after being ordered to vote for a new committee to consider a fresh system of appeals for MPs found to have broken the rules, only for the government to backtrack after the opposition parties refused to co-operate.
Labour leader Sir Keir Starmer said Johnson had chosen to hide away rather than address the mess he had created.
He said: “Boris Johnson does not have the decency either to defend or apologise for his actions. Rather than repairing the damage he has done, the Prime Minister is running scared."
The Liberal Democrats, who secured the emergency three-hour debate, said Johnson’s absence from the Commons chamber represented a “shocking failure of leadership”.
Chief whip Wendy Chamberlain accused him of trying to undermine the rules to avoid scrutiny of his own conduct – including over the refurbishment of his Downing Street flat.
She added: “A fish rots from the head down, and it’s the same with Boris Johnson’s corrupt and sleazy Government."
On Monday, during his visit to Hexham General Hospital, Johnson refused to be drawn on the events of last week.
However, he welcomed moves by the Commons Speaker to forge a cross-party consensus on reform of the way the standards system operates.
Johnson said: “I think it is very important that we get this right. We are going to hold MPs to account. MPs should not break the rules.
“If there is anything positive to come out of the whole thing it is that as far as I can make out the Speaker is determined to try to move us all forward with a system whereby we have a cross-party approach, which is what we were trying to achieve last week.”
Watch: Sir Keir Starmer tells MPs 'enough is enough' over PM's conduct