British Prime Minister Boris Johnson faced growing scrutiny Sunday following explosive accusations by his former chief aide Dominic Cummings earlier this week that he lacks competence and integrity.

Cummings, who stepped down as his top adviser in December, used a personal blog Friday to allege Johnson tried to solicit potentially illegal donations to renovate his publicly-funded Downing Street flat.

He also claimed the UK leader suggested blocking an internal inquiry into government leaks, because the culprit identified was a close friend of Johnson's fianc?e Carrie Symonds.

Johnson has attempted to brush off the allegations from former aide Dominic Cummings
Johnson has attempted to brush off the allegations from former aide Dominic Cummings POOL / JUSTIN TALLIS

Johnson's office has dismissed the damning accusations, insisting all "reportable donations" are transparently disclosed and that the prime minister "has never interfered in a government leak inquiry".

International Trade Secretary Liz Truss said Sunday the claims were "a massive distraction" and that she had been assured all rules have been fully complied with.

"This is tittle tattle that's being promoted and I don't think it addresses the key issues the people of Britain care about," she told Sky News.

But the charges, which follow weeks of stories about allegedly inappropriate lobbying and sleaze involving Johnson, his ministers and officials, have dominated news headlines and front pages this weekend.

Dominic Cummings quit as Johnson's top adviser last year after a scandal over breaching coronavirus restrictions
Dominic Cummings quit as Johnson's top adviser last year after a scandal over breaching coronavirus restrictions POOL / Jonathan Brady

Some Conservatives have joined the condemnation of Johnson, with former attorney general Dominic Grieve, a long-time critic, branding him "a vacuum of integrity".

They have also prompted the main opposition Labour Party to call for a "root and branch" independent inquiry into the use of taxpayers' money by Johnson's government.

"Whether I back Dominic Cummings' view or Boris Johnson's view, what we need is a proper independent inquiry where it isn't about two boys fighting and is about taxpayers in our country," Labour lawmaker Jess Phillips told Sky News.

She confirmed the party will pose an urgent question in parliament next week about the allegations surrounding Johnson's flat refurbishment.

Johnson is under pressure in parliament from the opposition Labour party
Johnson is under pressure in parliament from the opposition Labour party UK PARLIAMENT / JESSICA TAYLOR

Cummings, the controversial brains behind the 2016 campaign for Britain to leave the European Union, was appointed chief adviser by Johnson when he took power in July 2019.

He helped to secure a thumping election victory that December, but his frequent clashes with colleagues are said to have led to persistent tensions and he left government a year later.

Cummings' reputation had been severely damaged after he went on a lengthy cross-country journey with his family, claiming he and his wife needed help from relatives after they both developed Covid-19 symptoms, despite stay-at-home rules in force.

In his most serious claim Friday, Cummings wrote he had warned Johnson against plans to use Conservative Party donations in an "unethical, foolish, possibly illegal" way to renovate his Downing Street apartment.

Following months of controversy about the issue, a government minister said in a written parliamentary answer Friday that Johnson had met the costs "out of his own pocket", but it is unclear if he repaid a donor.

The Electoral Commission, which regulates donations to political parties and their spending, has confirmed it is investigating the matter.

Cummings ended his 1,000-word blog post by adding: "It is sad to see the PM and his office fall so far below the standards of competence and integrity the country deserves."

Cummings was responding to newspaper headlines reporting Downing Street staff blamed the ex-aide for leaking embarrassing text messages, including some that have embroiled billionaire inventor James Dyson in the growing Westminster lobbying scandal.

The Sunday Times reported Johnson may have personally briefed the newspaper editors, after deciding "to finger Cummings for the leaks".

"It is understood that he overruled advisers who warned him that the move was 'suicidal', it said.