Former attorney general Dominic Grieve has launched a blistering attack on Boris Johnson, saying he must explain how the refurbishment of his Downing Street flat was paid for.

It comes after the Prime Minister’s former top adviser, Dominic Cummings, accused Mr Johnson of plotting to get Tory donors to pay for the work amid reports he was given a donation of £58,000.

Mr Grieve – a long-standing critic of Mr Johnson – described the Prime Minister as a “vacuum of integrity” who must come now clean.

“It is all smoke and mirrors. He hasn’t said when he decided to repay it or whether he has now repaid it,” he told the BBC Radio 4 Today programme.

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“The fact is that he did get, I think it has become quite clear, a significant gift towards the refurbishment of the flat.

“If a minister goes abroad and gets given a gold watch by a foreign he has to hand it back to the Government or he has to buy it back. He doesn’t end up with £58,000 – if that’s figure – for refurbishing your private flat in Downing Street.

“My impression is there has been constant wriggling about the source of the money for this refurbishment.”

Meanwhile, Labour has called on the Government to release full details of how the refurbishment of Boris Johnson’s Downing Street flat was paid for.

The Government has said the Prime Minister paid for the work out of his own pocket, however his former top adviser Dominic Cummings accused Mr Johnson of wanting Tory donors to secretly fund the work.

Shadow communities secretary Steve Reed told the BBC Radio 4 programme: “We are calling for the Government to publish any correspondence relating to payments or donations around the refurbishment.

“We need to know the full amount that was spent and we need to know who paid for the work in the first place who the Prime Minister now proposes to reimburse.”

He added: “If people are making significant donations to the Conservative Party, to the Government, we need to know who they are so that we can make sure the Government isn’t doing favours for them in return.

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“That is what sleaze is all about. That is the behaviour of a tin pot dictatorship. Britain, frankly, deserves a lot better than that.”

In response to Mr Cummings’ claims about the funding of the flat refurbishment, the statement said: “At all times, the Government and ministers have acted in accordance with the appropriate codes of conduct and electoral law.

“Cabinet Office officials have been engaged and informed throughout and official advice has been followed.”

Earlier a Government statement said that Mr Johnson had met the cost of the flat refurbishment – which reportedly ran to £200,000 – out of his own pocket.

Former foreign secretary Lord Hague said he did not know if there was any truth in the claims but said that Downing Street would need to come up with some “good answers”.

“If all of these things were true, they would be damaging to anybody, including a prime minister,” he told Times Radio.

Labour deputy leader Angela Rayner said the Government was “lurching between cover-ups and cock-ups”.

“Labour is focusing on jobs, crime and the NHS, while the Conservatives are fighting each other like rats in a sack and slipping deeper and deeper into the mire of sleaze,” she said.