Ministers were not involved in a decision to refer Boris Johnson to the police over further potential coronavirus rule breaches, Justice Secretary Alex Chalk said.
Mr Johnson believes he is the victim of a “politically motivated stitch up” after the Cabinet Office passed to the police concerns over events in Chequers and Downing Street following a review of his official diary carried out ahead of the Covid public inquiry.
Mr Johnson’s office claims the handling of the situation has been “bizarre and unacceptable” and the events in question were within the rules.
“Many will conclude that this has all the hallmarks of yet another politically motivated stitch up.”
But the proper process has been followed and there was “no ministerial intervention”, Mr Chalk said.
The Cabinet Office said that ministers had “played no role” in the decision to pass information to the police, who were contacted prior to any minister being made aware.
The referral was instead made by officials acting within the Civil Service Code, it said.
The diary revealed visits by friends to Chequers during the pandemic and new allegations about Mr Johnson’s behaviour in Downing Street, The Times, which broke the story, said.
The Cabinet Office passed concerns to the Metropolitan Police and Thames Valley Police after the new information came to light during a review by taxpayer-funded lawyers.
The Privileges Committee, which is conducting an inquiry into whether Mr Johnson lied to Parliament about the partygate scandal, has also been informed.
“Material came to light which was passed to the civil service.
“The civil service considered that in accordance with their code, and with no ministerial intervention, I want to make that absolutely clear, that was then passed to the police.
“From the civil service’s point of view, if they sat on it and suppressed it, people would have criticised them. If they passed it on, that will raise questions as well.
“Ultimately, whether it was the right judgment to do it turns on what’s in those documents.”
It read: “No contact was made with Mr Johnson before these incorrect allegations were made both to the police and to the Privileges Committee. This is both bizarre and unacceptable.
“For whatever political purpose, it is plain that a last-ditch attempt is being made to lengthen the Privileges Committee investigation as it was coming to a conclusion and to undermine Mr Johnson.”
The Cabinet Office said: “Information came to light during the process of preparing evidence for submission to the Covid inquiry.
“It was identified as part of the normal disclosure review of potentially relevant documents being undertaken by the legal team for inquiry witnesses.
“In line with obligations in the Civil Service Code, this material has been passed to the relevant authorities and it is now a matter for them.”
A spokesman added on Wednesday: “The Cabinet Office has not made any assessment or conducted any investigation of the material that has been passed to the police.
“Ministers played no role in deciding whether the information should be handed over to the police. The police were first contacted on May 16 prior to any minister being made aware.”
Senior Tory MP Jacob Rees-Mogg, a Johnson loyalist, told GB News he visited Chequers with his family during the pandemic but the meeting was “entirely within the rules”.
He said: “I can tell you that during that period I went to Chequers. I was invited there with my children, entirely in accordance with the rules. Another senior government minister was going to come but the prime minister cancelled him because you were only allowed to have one family present at the time.”
The fallout adds to the problems facing Rishi Sunak, who was fined over a gathering in Downing Street during the pandemic along with Mr Johnson in June 2020.
Mr Sunak faces Prime Minister’s Questions later on Wednesday in which the subject of Mr Johnson’s past conduct could be raised.
Deputy Labour leader Angela Rayner said the revelations show the Tories are too “haunted by their own failure” to govern.
The Liberal Democrats have demanded Mr Sunak’s Government brings an end to the taxpayer-funded legal defence provided to Mr Johnson over the partygate probe.
The Government expects to pay an estimated £222,000 in legal fees to help Mr Johnson defend himself in the Privileges Committee inquiry.
Lindsay Jackson, spokeswoman for the Covid-19 Bereaved Families for Justice group, branded Mr Johnson “totally unfit for any form of public service” following the revelations and suggested he “quietly step back from public life”.