The Green Party has admitted that its leader Zack Polanski has, until recently, been living on a houseboat in London and may have failed to pay council tax.
In a statement given to the BBC, a party spokesperson said Polanski had "taken steps to pay any council tax he may be found to owe".
They added: "Zack apologises sincerely for the unintentional mistake."
Polanski has been under pressure to explain whether the houseboat, moored at a marina in east London, had been his primary residence.
A Waltham Forest Council spokesperson said it was assessing and taking legal advice over "complex factors unique to moorings".
It added: "We are working with Mr Polanski's team to establish the full picture, at which point we will be able to determine whether or not there is any council tax owed to Waltham Forest."
Tax lawyer Dan Neidle, who has investigated the tax affairs of several politicians, said a boat is liable for council tax when used as a person's "sole or main residence".
"If, as seems likely, that was his main residence, then Mr Polanski and his partner should have paid council tax there," Neidle wrote on his Tax Policy Associates website this week.
The Times newspaper last week questioned whether Polanski had paid the council charges for the boat for the past three years.
It reported that it had seen an advertisement to sell the boat in which Polanski's partner had said: "We are moving house and so will sadly be leaving the gorgeous community behind."
The advert, which the BBC has also seen, said the boat "has been our amazing home... for three years".
The paper said that the Green Party had told it Polanski lived in a room that he rented at a different address in London and council tax was included in his rent there. The party told the paper that he only stayed on the boat "occasionally".
However the Times reported that the Green Party leader and his partner "appear in recent years to have stayed on a narrowboat at a marina", adding a local launderette said it had often done laundry for Polanski and his partner from 2023 to 2025.
Polanski, along with several other individuals also thought to have boats in the marina, used a nearby building as a postal address. The marina is part of Waltham Forest borough council, and the Mail reported that he had been registered to vote there.
When the BBC asked the Green Party for clarification about Polanski's residence and whether he had paid the relevant council tax, a party spokesperson gave us a statement saying: "Until relatively recently, Zack was living on a houseboat, which came with its own unique practical circumstances and considerations."
It continued: "He has immediately taken steps to pay any council tax he may be found to owe. For security reasons, we do not comment publicly on Zack's address."
A Labour party spokesperson said: "After repeatedly claiming his council tax was all above board, Zack Polanski has been caught red-handed."
Conservative Party chairman Kevin Hollinrake said questions over his council tax showed "staggering hypocrisy".
He added: "A man who wants to hike taxes for millions has failed to pay his own council tax properly."
Last week Polanski acknowledged he was wrong to say he had been a spokesman for the British Red Cross while campaigning in 2022.
Polanski said he had hosted fundraisers for the charity in the past but accepted he had used "the wrong word" when describing himself as a spokesman.
Correction 12 May: This story has been updated to make clear that Zack Polanski's houseboat is in the Waltham Forest council area, and not in Hackney.
