British Prime Minister Boris Johnson's refurbishment of his Downing Street flat will be investigated by the Electoral Commission as the watchdog said it is satisfied there are "reasonable grounds to suspect that an offence or offences may have occurred".

Mr Johnson's troubles over the renovations dramatically deepened today when the commission said it would begin a "formal investigation" to see if any rules had been broken.

Speaking in parliament today, Mr Johnson denied breaking the rules over the refurbishment.

"I've conformed in full with the code of conduct and ministerial code," Mr Johnson said, as he came under sustained pressure to state who paid for the lavish revamp, and wider accusations of cronyism and favoured access.

Questions have been mounting for Mr Johnson since former aide Dominic Cummings accused him of wanting donors to "secretly pay" for the renovations to his No 11 residence in a "possibly illegal" move.

Downing Street has refused to say whether Mr Johnson received an initial loan from the Conservative Party to cover renovations to the flat at No 11.

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."

Mr Johnson is facing a stream of allegations in newspapers about everything from his muddled initial handling of the Covid-19 crisis to questions over the redecoration of the apartment.

The Daily Mail newspaper cited unidentified sources as saying that, in October, shortly after agreeing to a second lockdown, Mr Johnson told a meeting in Downing Street: "No more f***ing lockdowns – let the bodies pile high in their thousands."

Yesterday, UK Defence Secretary Ben Wallace flatly denied that report, saying to Sky News: "It's not true - it's been categorically denied by practically everyone," and added that Mr Johnson was focused on the Covid response.

Britain has the world's fifth worst official Covid-19 death toll, with 127,681 deaths, after the United States, Brazil, Mexico and India, according to Johns Hopkins University of Medicine.

Mr Johnson did impose a third lockdown, in January, though critics say it could have been avoided had he yielded to pressure from senior ministers to make the second lockdown more stringent.

We need your consent to load this rte-player contentWe use rte-player to manage extra content that can set cookies on your device and collect data about your activity. Please review their details and accept them to load the content.Manage Preferences