LONDON — An investigation has cleared British Prime Minister Boris Johnson of wrongdoing in the scandal over the redecoration of his official Downing Street residence, concluding that he knew “nothing about” how the project was financed until reports surfaced in the media.

But Christopher Geidt, whom Johnson appointed as independent adviser on ministerial standards last month, criticized the prime minister for “unwisely” failing to determine the source of funding for the pricey renovations. The project cost as much as 200,000 pounds ($233,000), according to news reports.

British prime ministers receive a government grant of up to 20,000 pounds to refurbish the official residence when they move in. Johnson had proposed setting up a charitable foundation to cover additional costs. When that was ruled inappropriate, Conservative Party donor David Brownlow paid the outstanding bill, Geidt said in his report. Johnson later reimbursed the money.

“I have also spoken … to the prime minister who confirms that he knew nothing about such payments until immediately prior to media reports in February 2021,” the report said. “At that point, the prime minister immediately sought the necessary advice about his interests and, as a consequence, settled the full amount himself on March 8, 2021.”

The “cash for curtains” scandal has dogged Johnson amid reports that he failed to report any outside financing as required by the rules governing the behavior of government ministers. The allegations provided fodder for pointed questions in Parliament and from the media, after newspapers suggested that the bills skyrocketed as the prime minister’s fiancée hired a celebrity interior designer and splashed out on items such as gold wallpaper and a sofa that sells for 15,000 pounds ($20,800).

“It is clear from the record that while a serious and genuine endeavor, the trust was not subjected to a scheme of rigorous project management by officials,” Geidt said. “Given the level of the prime minister’s expectations for the trust to deliver on the objects he had set, this was a significant failing.

“Instead, the Prime Minister — unwisely, in my view — allowed the refurbishment of the apartment at No. 11 Downing Street to proceed without more rigorous regard for how this would be funded.”

A spokesman for the prime minister said the report confirmed that Johnson had not violated the ministerial code and he has now “made a declaration” about the project on his list of ministerial interests.

“Cabinet Office officials were engaged and informed throughout and official advice was followed,” the prime minister’s office said. “Other than works funded through the annual allowance, the costs of the wider refurbishment of the flat are not being financed by taxpayers and have been settled by the prime minister personally.”

The opposition Labour Party quickly criticized Johnson.

“The Conservatives think it’s one rule for them and another for everyone else,” Angela Rayner, the party’s deputy leader.