The Commission said there were "reasonable grounds to suspect that an offence or offences may have occurred", but insisted its inquiry into the affair was related to the Conservative Party and not the Prime Minister personally.
Still Mr Johnson continued to face questions over the redecoration of his Downing Street flat. It is claimed £58,000 of donated party funds was used for the redecoration, yet no such donation had been declared to the Electoral Commission.
Sir Keir Starmer challenged Mr Johnson at Prime Minister’s Questions in a heated exchange that saw the PM insist he paid for the renovations himself.
The Labour leader said: “The House will have heard the Prime Minister’s answer and I remind him that the ministerial code says, and I quote, ‘ministers who knowingly mislead Parliament will be expected to offer their resignation'”.
“Who initially, and Prime Minister, initially is the key word here, who initially paid for the redecoration of his Downing Street flat?”
Mr Johnson evaded answering the actual question, instead insisting he had paid for the works.
He said: “As for the latest stuff that he is bringing up, he should know that I have paid for Downing Street refurbishment personally.
“And I contrast it … any further declaration that I have to make, if any, I will be advised upon by [ministerial standards adviser] Lord Geidt.”
Sir Keir refused to back down on the subject, offering Mr Johnson “multiple choice” answers.
He said: “Either the taxpayer paid the initial invoice, or it was the Conservative Party, or it was a private donor, or it was the Prime Minister.”
The Labour leader then turned to whether Lord Brownlow made a contribution to cover the cost.
Mr Johnson answered: “I think I have answered this question several times now and the answer is that I have covered the cost.
“I have met the requirements that I have been obliged to meet in full.”
The Prime Minister had earlier denied saying he would rather see “bodies pile high” than implement a second lockdown in October.
Sir Keir had said: “It was reported this week, including in the Daily Mail, the BBC and ITV – backed up by numerous sources – that at the end of October the Prime Minister said he would rather have, and I quote, ‘bodies pile high’ than implement another lockdown.
“Can the Prime Minister tell the House categorically yes or no – did he make those remarks or remarks to that effect?”
Mr Johnson answered: “No. And as a lawyer, I am given to understand, and I think if he is going to repeat allegations like that he should come to this House and substantiate those allegations, and say where he heard them and who exactly is supposed to have said those things."
Sir Keir also listed the principles meant to govern those in public office, he said: “Selflessness, integrity, objectivity, accountability, openness, honesty and leadership.
“Instead, what do we get from this Prime Minister and Conservative government?
“Dodgy contracts, jobs for their mates and cash for access – and who is at the heart of it? The Prime Minister – major sleaze sitting there.”
The verbal attack comes with Mr Johnson facing new rules that would force him to correct misleading statements to Parliament after the Commons Speaker backed demands for tougher action to promote honesty in politics.
Sir Lindsay Hoyle is backing a proposal for the cross-party Commons Procedure Committee to look into “how perceived inaccuracies could be corrected” as quickly as possible.
Opposition party leaders had written to the Speaker angry over the multiple occasions where Mr Johnson had made inaccurate statements in the Commons.
These included on things Sir Keir has said, on carbon emissions, economic growth, nurses’ bursaries, hospital car parking, NHS spending, the Covid-19 track and trace app, and poverty.
Ministers are required to correct the record at the despatch box as soon as possible if they have made misleading statements to the Commons, but Mr Johnson has failed to do so repeatedly.
The Prime Minister’s former press secretary Allegra Stratton also refused 20 times to correct the record or apologise at the time.
A spokeswoman for the Speaker’s Office said: “Mr Speaker welcomed the meeting and the proposal to ask the Procedure Committee to look into how perceived inaccuracies could be corrected.
“He hoped such a measure would improve transparency in House of Commons proceedings.”
The Procedure Committee added: “The committee will consider any request it receives to look at the matter of ministerial corrections in the new session of Parliament.”
There was further outrage on Wednesday afternoon after it emerged Mr Johnson would himself decide whether he broke any rules.
Downing Street announced a new “independent adviser” on ministerial standards Lord Geidt would lead an investigation into makeovers funding.
However, the Prime Minister’s spokesman confirmed on Wednesday the PM would remain the “ultimate arbiter” of whether he broke the ministerial code.
The spokesman said: "As the ultimate arbiter of the code, the responsibility for deciding on an investigation and the drawing of final conclusions from it rightly remains the responsibility of the Prime Minister. That's been the case under successive governments."
Asked if Mr Johnson would recuse himself, the spokesman said: "The code's very clearly set out on that, with regards the role of the Prime Minister in this, and that hasn't changed."
The role of ministerial standards adviser has been vacant since the resignation of Sir Alex Allan in October, who resigned after Mr Johnson overruled him on an investigation into home secretary Priti Patel's behaviour.