The Green party leader, Zack Polanski, has admitted he may have failed to pay the correct council tax while living on a London houseboat.

Polanski had faced mounting questions over whether the houseboat, moored in east London, was his primary residence.

A Green party spokesperson described the situation as an “unintentional mistake” and said Polanski had “immediately taken steps” to pay any tax owed.

The spokesperson said: “Until relatively recently, Zack was living on a houseboat, which came with its own unique practical circumstances and considerations. He has immediately taken steps to pay any council tax he may be found to owe. Zack apologises sincerely for the unintentional mistake.”

The Green party previously told the Times newspaper that Polanski rented a room at another address where council tax was included in the rent and stayed on the boat only “occasionally”. Government guidance states that a person may be liable for council tax on a boat if it is their “sole or main” residence.

A Green party spokesperson said: “For security reasons, we do not comment publicly on Zack’s address. There have recently been two serious incidents which have been reported to the police and are under investigation.”

The Times last week reported seeing an advertisement for the sale of the boat in which Polanski’s partner wrote: “We are moving to a house and so will sadly be leaving the gorgeous community behind.”

The Daily Mail separately reported that Polanski was registered to vote at a building near the marina, which he is also said to have used as a mailing address.

Dan Neidle, a tax lawyer and founder of Tax Policy Associates, analysed Polanski’s situation this week and wrote: “If the boat was in fact Mr Polanski’s ‘sole or main residence’ then he and/or his partner should have registered for, and paid, council tax for those three years.”