The Prime Minister was criticised for failing to promptly disclose how a private 10-day holiday to Mustique was funded.
He was found to have breached the code of conduct by the Commons Standards Commissioner with the £15,000 luxury Caribbean holiday, only for MPs to overrule the finding.
Kathryn Stone claimed the Prime Minister had not “fulfilled conscientiously” the requirements for registering the trip’s funding.
Ms Stone explained it was “unusually difficult to find the facts” about the holiday during her investigation, which lasted more than a year.
She added she could not find “any reliable documentary” that clearly outlined how the trip with wife Carrie between December 26 2019 and January 5 last year was paid for.
Ms Stone added: “Because he did not make sufficient inquiries to establish the full facts about the funding arrangements for his free accommodation, either before his holiday, as he should have done, or in 2020, I find that Mr Johnson has not fulfilled conscientiously the House’s requirements for registration.”
However, MPs on the Commons Committee on Standards thought differently and cleared him of the allegation.
They said Carphone Warehouse founder David Ross was the donor as stated so the Prime Minister’s “register entry is accurate and complete”.
In a statement, it said: “This matter could have been concluded many months ago if more strenuous efforts had been made to dispel the uncertainty.
“It is regrettable that a full account and explanation of the funding arrangements for Mr Johnson’s holiday accommodation has only come to light as a result of our own inquiries rather than at an earlier stage.
“If greater clarity had been made available to the commissioner at the first instance, this matter could have been cleared up many months ago.”
Labour deputy leader Angela Rayner said: “This whole murky affair shows Boris Johnson has a casual relationship with the truth and a flagrant disregard for the most basic standards of integrity and trustworthiness that we would expect from a Prime Minister.
“The way Johnson handles his personal finances mirrors the way he governs the country – chaos and confusion.”