The prime minister has been issued with a county court judgment for a debt of £535, it has been revealed.
An "unsatisfied record" registered to Boris Johnson at "10 Downing Street" can be found on the county court judgments database.
First reported by Private Eye magazine, it is dated 26 October 2020.
The identity of the creditor and the nature of the debt are not disclosed in the records.
"I have seen that report, we are looking into this issue," the PM's spokesman said when asked about it at a regular briefing with journalists.
The judgment was issued less than two weeks after a Conservative Party donor told the party he was making a donation of £58,000 over refurbishments to Mr Johnson's Downing Street flat.
The PM has repeatedly said he paid for the refurbishment of the private flat above Number 11.
But he has refused to answer whether he paid for the initial cost or whether a donor or the Conservative Party funded it and he paid the amount back.
Both Number 10 and the Conservative Party have not denied reports that the Conservative Campaign Headquarters (CCHQ) paid the Cabinet Office to cover initial costs of the works.
The furore has sparked a number of inquiries, including from the Electoral Commission into whether any donations or loans were properly declared.
It has said there are "reasonable grounds" to suspect an offence or offences had been committed.
Mr Johnson's spokesman said the debt has "nothing to do with" the refurbishment.
"All such bills have been duly paid either by the government or the prime minister personally," he said.
Asked if the PM could be trusted to handle the nation's finances if he could not take care of his own, Mr Johnson's spokesman said: "I think our record on the economy is very clear."
"You should not be concerned, no," said the PM's press secretary when asked if people should be worried about Mr Johnson's finances.
Labour's deputy leader Angela Rayner said: "Another day, another report of deeply concerning irregularities about the renovation of Boris Johnson's flat.
"This is not about Boris Johnson's personal finances, the record speaks for itself that he has already broken the rules on declaring his financial interests, and he is already under investigation regarding potentially illegal wrongdoing.
"The issue of debt when it comes to the prime minister is whatever debt of gratitude Boris Johnson owes to the Tory donor who paid to renovate his flat, and what this donor or donors were promised or expected in return for their generosity."
Bailiffs can be sent round if judgments are not paid, the government website states.
The information can also be used by banks and loan companies to decide whether to issue credit or loans.
"If you're late with your payments, you could be taken back to court and you may have to pay extra costs," the website says.
Such judgments can be issued if someone opts for court action against an individual and there is no response.
It means the court has formally decided that the money is owed.