Rishi Sunak has been told the Tory "addiction to sleaze and scandal" has "done huge damage to this country" - as he was branded "too weak" to deal with deputy Dominic Raab.
The PM sat side-by-side with Mr Raab, who faces multiple accusations of bullying, as he faced tough questions amid calls to remove him.
In a heated PMQs exchange, Keir Starmer cited The Mirror's story about the impact the deputy Prime Minister's alleged behaviour had on victims.
He told MPs that some of those affected were claimed to have felt suicidal, and asked the PM: "How would he feel if one of his friends were forced to work for a bully because the man at the top was too weak to do anything about it?"
The PM was branded "weak" for his handling of complaints about Mr Raab, and for his slow response to Nadhim Zahawi's breaches of the ministerial code.
Mr Sunak was also branded "pathetic" over his failure to prevent widespread strike action and told to "put his foot down" over the huge taxpayer bill for defending Boris Johnson in a Partygate probe.
In a scathing broadside, Mr Starmer fumed: "After 13 years in power, trying to blame the Labour Party for his failure to sort out the strikes is rank pathetic.
"The Tory Party's addiction to sleaze and scandal has done huge damage to this country and the cost to the public keeps adding up.
"We've got a justice system letting murderers walk the street, heart attack victims waiting hours for an ambulance, an economy that is shrinking quicker than his leadership, and even I couldn't quite believe it when I saw that his Government is expecting taxpayers to pay the legal fees for the member for Uxbridge (Boris Johnson) defending himself over his lockdown rule-breaking."
Last week it emerged that the cost of the former Prime Minister's legal defence had soared to an enormous £220,000.
Addressing the cost of defending Mr Johnson over an allegation he misled Parliament, Labour leader Keir Starmer said: "Surely even this Prime Minister can put his foot down and stand up to his old boss and say he made this mess, he can pick up the bill?"
The Prime Minister snapped back accusing the Labour leader of "carping from the sidelines" and "failing to lead", citing criticism by Labour MP Rosie Duffield who said being in the party "had reminded her of being in an abusive relationship.".
Mr Sunak claimed he acted swiftly and decisively after his ethics advisor Sir Laurie Magnus found former party chairman Mr Zahawi had committed multiple breaches of the ministerial code.
Mr Starmer pointed out that "anyone picking up a newspaper in July last year" would have been aware that Mr Zahawi's financial affairs were being investigated.
The Labour boss said the PM has been slow to act, telling MPs: "So in relation to his former chair, his defence is: nobody told me, I didn't know, I didn't ask any questions. Is the Prime Minister now also going to claim that he's the only person completely unaware of serious allegations of bullying against the Deputy Prime Minister before he appointed him?"
Mr Sunak replied: "The honourable gentleman ask these questions about what was known and I followed due process, I appointed an independent adviser as soon as I was made aware of new information."
The Prime Minister is under pressure to suspend his deputy, Mr Raab who is subject to an ongoing bullying investigation.
Downing Street declined to rule out suggestions Rishi Sunak had been warned informally about allegations surrounding Dominic Raab before appointing him as Deputy Prime Minister.
The Prime Minister's press secretary repeatedly said that "the PM was not aware of any formal complaints at the time of appointing Dominic Raab" - even in response to questions about whether he'd known about informal complaints.
Pressed further, she said: "I don't know what your definition of informal complaints is. The PET (propriety and ethics team) processes are very clear.
"The appointments and usual processes were followed and we were not aware of any formal complaints."
The Mirror revealed that civil servants claim they suffered breakdowns and felt suicidal over the Deputy PM's alleged conduct- with staff saying working the Tory felt like being in a “controlling and abusive relationship”.
Mr Raab is being investigated over eight complaints during his time at the Ministry of Justice, the Foreign Office and the former Brexit department, which are said to involve at least 24 staff. He denies accusations of bullying.
Phillip Rycroft, the former top official at the Department for Exiting the EU, confirmed he had given evidence to the probe led by top KC Adam Tolley.
He told Times Radio: "I'm pleased the investigation is happening.
"Clearly for everybody involved in this getting this sorted out is long overdue, but we'll have to wait and see what the investigator comes up with and ultimately the decision on the basis of that evidence is one for the Prime Minister."
Dave Penman, leader of the FDA union, which represents senior officials, said Mr Raab should be suspended to protect other members of staff while the investigation is conducted.
"Dominic Raab is now facing investigations around eight separate complaints involving what we understand is dozens of civil servants in three separate government departments over a period of four years," he told BBC Radio 4's Today programme.
"If that was any other employee, if that was a permanent secretary in the civil service, they would in all likelihood be suspended from their job while the investigation took place.
"That's not to prejudge the investigation, that's to say if there are serious allegations of bullying and extensive allegations like this, that one of the considerations is how do you protect employees from that sort of behaviour?
"And while it's being determined, you would normally suspend someone, given the seriousness and extent of those accusations."