Already facing a campaign of damaging leaks by a former key adviser, British Prime Minister Boris Johnson is now under formal investigation by the country’s Electoral Commission.

The commission has confirmed it is looking into the financing of the redecoration of Mr Johnson’s apartment, saying there were grounds to suspect an offence might have been committed.

The PM reportedly spent £200,000 ($357,000) to refurbish the apartment above 11 Downing Street, where he lives with fiancee Carrie Symonds.

The couple moved to the four-bedroom property in 2020 and spent parts of lockdown giving the place a makeover.

Ministers have said Mr Johnson paid for the work himself, but it is unclear when he paid, and whether the refurbishment was initially financed by a loan by a Conservative Party donor or donors.

Under political financing rules, Mr Johnson would have been required to declare the donation.

Number 11 has undergone significant renovations by leaders and their families over the years. Photo: HM Treasury 

Probe could result in police action

As Prime Minister, Mr Johnson has an annual taxpayer-funded £30,000 ($53,600) allowance to maintain and furnish his official residence.

Anything above that must be met by him personally.

“We are now satisfied that there are reasonable grounds to suspect that an offence or offences may have occurred,” the Electoral Commission said.

Floor plans for Number 10 and 11 Downing Street. Photo: British History Online

“We will therefore continue this work as a formal investigation to establish whether this is the case.”

If it finds that an offence has occurred, and that there is sufficient evidence, the commission can issue a fine or refer the matter to the police.

Upmarket designer and $1500-a-roll wallpaper

Mr Johnson’s former adviser Dominic Cummings claims the PM hatched a scheme to get Conservative Party donors to pay for the makeover of the apartment by Lulu Lytle, an upmarket interior designer.

Mr Cummings said he had told Mr Johnson such plans were “unethical, foolish, possibly illegal”.

Boris Johnson and Carrie Symonds hired designer Lulu Lytle whose home makeovers often include rattan and luxurious wallpaper. Photo: Instagram

The Daily Mail then reported it had seen leaked emails showing party donor Lord Brownlow put £58,000 ($103,770) towards the refurbishment.

Under questioning in parliament from opposition Labour Party leader Keir Starmer, who cast Mr Johnson as “Major Sleaze”, the PM said he had covered the costs and had followed in full the code of conduct and ministerial code.

“The answer is I have covered the costs,” Mr Johnson said.

Mr Starmer had accused the PM of spending his time selecting wallpaper for £840 ($1500) a roll in the middle of the pandemic.

Northern Ireland leader quits after party revolt

Meanwhile, backing Mr Johnson over post-Brexit trade rules has resulted in the resignation of Northern Ireland leader Arlene Foster, adding to the political disarray.

Mrs Foster has announced her resignation after party members mounted a push to oust her for her handling of the fallout from Brexit and other issues.

She will step down as leader of the Democratic Unionist Party on May 28 and as First Minister of Northern Ireland at the end of June.

Mrs Foster’s position became untenable after many DUP politicians signed a letter of no-confidence.

Mrs Foster and other prominent DUP politicians are facing the wrath of party members for backing the divorce agreement that Mr Johnson struck with the EU.

The arrangements have angered Northern Ireland’s British unionists, who say the new checks amount to a border in the Irish Sea and weaken ties with the rest of Britain.

-with AAP