A senior minister has said Boris Johnson did pay for the refurbishment of his official Downing Street flat out of his own pocket but was unable to say where he got the money.

International Trade Secretary Liz Truss said she had been assured the rules for ministers had been fully complied with and that the details would be declared publicly.

However, Labour called on the Electoral Commission to mount a full investigation after Mr Johnson’s former top adviser Dominic Cummings claimed he tried to get Tory donors secretly to fund the work.

Deputy leader Angela Rayner said there was a “real stench” around the Government and called on Mr Johnson to go to Parliament on Monday to explain what happened.

Ms Truss – who is the first minister to speak publicly since Mr Cummings issued his incendiary claims on Friday – dismissed the allegations as “tittle tattle”.

“I have been assured that the rules have been fully complied with and I know that he has met the costs of the flat refurbishment,” she told Sky News’ Sophy Ridge on Sunday programme.

“I absolutely believe and trust that the Prime Minister has done that.

“What people want to know is that in line with the rules the Prime Minister has met the cost of this refurbishment. That has happened. All the costs will be declared in line with the rules.

“That, as far as I am concerned, completely answers that question.”

Labour, however, insisted that Mr Johnson still had questions to answer as to how exactly he was able to meet the reported £200,000 cost of the refurbishment.

According to a leaked email obtained by the Daily Mail, the Tory peer Lord Brownlow said he was making a £58,000 donation to the party “to cover the payments the party has already made on behalf of the soon to be formed ‘Downing Street Trust’”.

The Electoral Commission – which first raised the issue with the Conservative Party more than a month ago – has said it is still looking into whether any of the sums relating to the work on the flat should have been declared under the rules on political donations.

Ms Rayner said the commission should now launch a full inquiry and she called on the Prime Minister to publish the latest register of ministers’ interests which was now eight months overdue.

“These are serious allegations,” she told BBC1’s The Andrew Marr Show.

“Why are they hiding the fact that ministers have to declare these donations and they’ve not done that? That’s serious. This is a real stench around what (the) Government is about.”

Mr Cummings launched his onslaught after he was accused by No 10 of being responsible for a series of damaging leaks.

Ministers are now concerned at what he may say when he gives evidence to MPs investigating the Government’s response to the pandemic next month.

He is widely known to have been critical of Mr Johnson’s delay in launching a second lockdown in England when cases began rising last autumn.

Among the allegations in his blog post was a claim the Prime Minister wanted to halt an inquiry into the leak of the plans which effectively bounced him into going ahead with it.

He said Mr Johnson had been concerned he would have “very serious problems” with his fiancee Carrie Symonds after a close friend of hers was implicated in the probe.

Ms Truss confirmed that, almost six months on, the investigation by the Cabinet Secretary Simon Case was still ongoing.

She dismissed charges by Mr Cummings that the whole episode showed that Mr Johnson lacked “competence and integrity”.

“This is tittle tattle that is being promoted and I don’t think it really addresses the key issues that people in Britain care about,” she said.

“The Prime Minister, who I work very closely with, has consistently through this crisis acted in the best interests of the country.

“These noises off are simply not helpful, they are not contributing to a positive future and they don’t reflect what is actually going on in Downing Street.”