A refit to the premises caused controversy earlier this year after leaked emails appeared to show that Conservative party donors had put up money for the project - a charge denied by No. 10.
However in an explosive blog post by his former aide, Mr Cummings has alleged that the Boris Johnson stopped discussing the matter with him after he questioned the ethics of soliciting funds to do up the residence shared by the PM, his partner Carrie Symonds, and their baby Wilf.
Referring to suggestions that he was behind the leaking of information around the financing of the project, Mr Cummings wrote: “The PM stopped speaking to me about this matter in 2020 as I told him I thought his plans to have donors secretly pay for the renovation were unethical, foolish, possibly illegal and almost certainly broke the rules on proper disclosure of political donations if conducted in the way he intended. “
He added: “I refused to help him organise these payments. My knowledge about them is therefore limited.
“I would be happy to tell the Cabinet Secretary or Electoral Commission what I know concerning this matter. “
In March the Electoral Commission was forced to investigate reports the Conservative party had put forward a £60,000 payment for the renovation of the prime ministerial address.
At the time Johnson fell short of denying reports he had sought donors to pay for the refurbishment, saying that “all such inquiries will be answered with normal declarations in the normal way”
However Downing Street has since said the PM paid for the work on the flat above Number 11 where he lives out of his own pocket.
In a statement to parliament provided on the same day as Mr Cummings’ attack, Cabinet Office minister Lord True said that works took place during the 2020/21 financial year on painting, sanding and floorboards in the flat.
He did not give a figure for the spending, but said: “Any costs of wider refurbishment in this year have been met by the prime minister personally.”
Labour’s Rachel Reeves MP, called for a full investigation into the claims made by the PM’s former aide.
She said: “There is something deeply suspect about how Boris Johnson and the government have been trying to cover up the luxury refurbishment of No.10.
“Throughout the course of the last year the government has been repeatedly evasive about who has been paying for the refurbishment. That leaves far too many questions marks over potential special favours that could have been cashed in on the back of that donation.
“Given we know it only takes a text from one of the Prime Minister’s chums to get a tax break, what might a discreet donation for a luxury refurbishment might get you?”
A No 10 spokesperson 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.
“All reportable donations are transparently declared and published – either by the Electoral Commission or the House of Commons registrar, in line with the requirements set out in electoral law.
“Gifts and benefits received in a ministerial capacity are, and will continue to be, declared in transparency returns.”