Boris Johnson has repeatedly dodged questions about who initially paid for the refurbishment of his Downing Street flat.
Speaking during PMQs on Wednesday, Labour leader Keir Starmer asked “who paid the initial invoice” for the renovations, which reportedly cost £200,000.
But the prime minister would only say he had “covered the cost”, with no reference to who paid the bills up front.
The Electoral Commission has launched a “formal investigation” to see if any rules have been broken.
Downing Street has refused to say whether Johnson received an initial loan from the Conservative Party to cover the renovations to the flat.
Dominic Cummings, Johnson’s former top adviser, has accused the PM of wanting donors to “secretly pay” in a “possibly illegal” move.
Starmer asked Johnson in the Commons: “Who initially – and, prime minister, ‘initially’ is the key word here – who initially paid for the redecoration of his Downing Street flat?
“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.”
Johnson said he had “paid for the Downing Street refurbishment personally”.
“I think I have answered this question several times now and the answer is that I have covered the cost,” he added.
Starmer, in reply, listed the seven “Nolan principles” that are supposed to govern politicians holding government office: “Selflessness, integrity, objectivity, accountability, openness, honesty and leadership.”
“Instead, what do we get from this prime minister and Conservative government?” he asked.
“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.”
Johnson angrily accused Labour of “playing political games” and said he had “met the requirements that I have been obliged to meet in full”.
Labour MP Lilian Greenwood said Johnson was “ranting and raving like a toddler who isn’t getting their own way”.
Prime ministers are allocated a taxpayer-funded budget of up to £30,000 a year to renovate the home – which is more than the median UK household income after tax. Any extra expense has to be paid for with non-taxpayer money.
The Electoral Commission can issue fines of up to £20,000, and if it is satisfied beyond reasonable doubt that an offence has occurred will in most cases draw the line at imposing its own sanction.
But it can also refer investigations to police or prosecutors under the Political Parties, Elections and Referendums Act 2000.