Boris Johnson’s independent ethics adviser has said the PM acted “unwisely” in the handling of his flat refurbishment but found that despite a “significant failing” in his approach, there was no breach of the ministerial code.

Mr Johnson pressed ahead with the lavish renovation of the 11 Downing Street flat without knowing how it would be paid for, and remained in the dark about its funding until controversy blew up in the media, found Christopher Geidt.

But despite bills totalling tens of thousands of pounds being handed over by the Conservative Party and wealthy Tory donor Lord Brownlow, the adviser found that Mr Johnson was not aware of the payments and there was no “reasonably perceived” conflict of interest.

The report sparked calls for reform of the system of oversight of ministerial interests from the former head of the government legal service, Sir Jonathan Jones, who quit last year over Mr Johnson’s threat to break international law over post-Brexit arrangements for Northern Ireland.

Sir Jonathan said: “I have no basis for questioning Lord Geidt’s approach to his task or to the evidence. But there is something unsatisfactory about a process that concludes ‘things went wrong, people acted unwisely, but no rules were broken’ … the ‘system’ failed but no one is responsible.

“Which confirms we need a better process.”

And Labour’s deputy leader Angela Rayner said: “The Conservatives think it’s one rule for them and another for everyone else.

“It’s staggering that the prime minister could rack up a £200,000 bill for a luxury refurbishment yet have no knowledge of how it was eventually paid. We know this isn’t the only aspect of the prime minister’s lifestyle that may be being funded by Tory donors – No 10 must now come clean about how far this goes.”

She called for the publication of all government documents relating to Lord Brownlow to establish whether any conflict of interest existed.

The report into the flat was published alongside the much-delayed register of ministerial interests, five months overdue after its publication date in December was missed because of the ressignation of Lord Geidt’s predecessor Sir Alex Allan when Mr Johnson overruled his bullying finding against Priti Patel.

The new adviser made clear he is ready to accept the scrapping of the principle that breaches of the ministerial code of conduct should automatically result in resignation or dismissal, describing the convention as “disproportionate”.

Neither the report nor the register reveal the actual cost of the refurb, carried out for Johnson and his fiancee Carrie Symonds to plans by interior designer Lulu Lytle and reported to have run to as much as £200,000.

Lord Geidt said that the financial assistance from Conservative Campaign Headquarters and Lord Brownlow, who is known to have signed a cheque for £58,000, amounted to a private interest.

But he added: “I have considered the nature of that support and am content that no conflict (or reasonably perceived conflict) arises as a result.”

Assistance from his party put the prime minister under no additional obligation, while there was “no evidence” that Lord Brownlow acted with “anything other than altruistic and philanthropic motives”, he ruled.

Lord Geidt said that plans to create a trust to fund the PM’s share of the maintenance and refurbishment of the flat were “not subjected to a scheme of rigorous project management by officials”.

And he added: “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.”

Over recent years, the taxpayer has provided up to £30,000 a year for maintenance and renovation of the PM’s private quarters in Downing Street, with the prime minister footing any additional bill from his or her own pocket

Lord Geidt’s report confirmed there were discussions soon after Mr Johnson’s arrival in Downing Street in July 2019 about creating a Downing Street Trust to cover the extra costs.

As the body had not been established by the time work began on the flat in April of last year – while Mr Johnson was in hospital with Covid – invoices were paid for by the Cabinet Office and then charged to the Conservative Party in anticipation of the trust repaying the amount.

The report found no evidence of Mr Johnson “being aware either of the existence of these invoices or how they were settled”.

Official advice was initially that the trust plan “while not straightforward, could be made to work”. But legal advice in June raised doubts over the idea.

Multimillionaire businessman Lord Brownlow was appointed to chair the trust in July and in October settled a supplier’s invoice himself, the report found.

Both Mr Johnson and the others involved assured Lord Geidt that at no point in the eight months until press reports appeared in February this year was the prime minister made aware of “either the fact or the method of the costs of refurbishing the apartment having been paid”.

It was only as controversy blew up in the media that Mr Johnson became aware of the arrangements and settled the full amount himself on 8 March.

Lord Geidt – former private secretary to the Queen – said that under normal circumstances, a prime minister “might reasonably be expected to be curious” about the financial arrangements. But he said that in the midst of the pandemic, Mr Johnson “simply accepted that the trust would be capable of satisfactorily resolving the situation without further interrogation”.

He was “ill-served” by officials, and cabinet secretary Simon Case has recognised “shortcomings” in the management of the project and in the failure to advise Mr Johnson earlier of the problems with the establishment of the trust.

Lord Geidt ruled: “Having advised that the interests declared by the prime minister present no actual or perceived conflict, I consider them to be consistent with the provisions of the ministerial code.”

He said that the interests had now been properly declared by Mr Johnson and accepted that any delay in making the declaration was due to the fact that the PM “reasonably assumed” that the issue was dealt with by the creation of a trust.

A No 10 spokesperson said:  “Lord Geidt’s independent report shows the prime minister acted in accordance with the ministerial code at all times. 

“The prime minister has made a declaration in his list of ministerial interests, as advised by Lord Geidt.

 “Cabinet Office officials were engaged and informed throughout and official advice was followed. 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.”