Ukip has dismissed claims that party leader Paul Nuttall used an empty house as his home address on electoral documents nominating him as a by-election candidate.
A spokesman for Ukip described a Labour allegation that Mr Nuttall had used the rented property to pretend to live in the Potteries as "hot air" which showed his opponents feared losing at the polls.
Staffordshire Police said "considerable media interest" in an allegation relating to a candidate standing in the Stoke-on-Trent Central by-election had prompted officers to launch an investigation.
Amid Labour claims that the allegations against Mr Nuttall meant he had serious questions to answer, Ukip said there had been no intention to deceive anyone and that Mr Nuttall was using the property in Penkhull, Stoke-on-Trent, as a place to live ahead of the poll.
The Ukip spokesman said: "The flat was rented before close of nominations, which was yesterday.
"Now he's formally a candidate and the campaign is under way, Mr Nuttall finally has an opportunity to move in, which he will do tonight.
"He plans to spend a lot of time in Stoke-on-Trent campaigning and will be using the flat as his base. If he's successful he will find a permanent home in the constituency."
The Labour MP for Stoke-on-Trent North, Ruth Smeeth, said in a statement: "The shocking allegations that Paul Nuttall has been using an empty house as his official address raise serious questions about his fitness for public office.
"There would be no reason to do this except to deliberately mislead the people of Stoke-on-Trent about where he actually lives. He should be open and honest about this.
"The people of Stoke-on-Trent need a strong, local MP who will fight for the issues that matter locally, not a man who is willing to treat them like fools."
A spokeswoman for the Electoral Commission said: "There is no requirement for a Parliamentary candidate to be resident in the constituency where they are standing for election.
"It is an offence under s65A of the Representation of the People act 1983 to knowingly provide false information on a nomination paper. It is for the police to investigate any allegations of an offence."
Speaking to Channel 4 News, Mr Nuttall said of the property: "It's not empty. People are in it now. I'll be in there and I'll be there for the rest of the campaign.
"It's not a false declaration at all. People are in the process of moving us in."
A Stoke-on-Trent City Council spokesman said: "We follow guidance from the Electoral Commission which is the independent body which oversees how elections are administered, and are following their advice in relation to this matter."