The Electoral Commission will investigate the refurbishment of Boris Johnson’s Downing Street flat, saying it was “satisfied that there are reasonable grounds to suspect that an offence or offences may have occurred”.
It comes as Mr Johnson is preparing to be grilled by MPs as he battles allegations over the funding of refurbishments to his Downing Street flat and remarks over coronavirus lockdowns.
He will appear at Prime Minister’s Questions at 12pm today for the first time since former aide Dominic Cummings accused him of wanting donors to “secretly pay” for the renovations in a “possibly illegal” move.
Mr Johnson will be subjected to questions from Labour leader Sir Keir Starmer as the Prime Minister also faces pressure over allegedly saying he would rather see “bodies pile high” than impose a third shutdown.
An Electoral Commission spokesperson said: “We have been in contact with the Conservative Party since late March and have conducted an assessment of the information they have provided to us.
“We are now satisfied that there are reasonable grounds to suspect that an offence or offences may have occurred. We will therefore continue this work as a formal investigation to establish whether this is the case.
“The investigation will determine whether any transactions relating to the works at 11 Downing Street fall within the regime regulated by the Commission and whether such funding was reported as required.
“We will provide an update once the investigation is complete. We will not be commenting further until that point.”
Downing Street has refused to say whether Mr Johnson received an initial loan from the Conservative Party to cover renovations to his residence in No 11.

Labour has accused him of having “lied” over the funding, and accused senior members of the government of a possible “cover-up”.
Transport Secretary Grant Shapps insisted a review into the controversy by Cabinet Secretary Simon Case will answer whether the Tory party gave Mr Johnson a loan, before the Prime Minister paid back the costs.
“I just don’t have the answer but the Cabinet Secretary will and it will be transparently produced in the annual report and the accounts of the Cabinet Office,” the Cabinet minister told Times Radio.
But Mr Shapps declined to say whether he would have approved the funding when he was party chairman, instead telling BBC Breakfast: “My side of things was the campaigning side of things, I didn’t get involved with the fundraising side of things.”