Police have said there is "insufficient evidence" of criminal activity after claims a former UKIP leader misled by-election voters about his address.
Last year, Labour said Paul Nuttall - a candidate for Stoke-on-Trent Central - used a house he had yet to stay in as his address on nomination papers.
UKIP said at the time that all electoral law was "complied with".
Staffordshire Police said it had conducted a "thorough" investigation into the allegations.
In a statement, the force said: "After full consultation with the Crown Prosecution Service a decision has been made that there is insufficient evidence that criminal offences had been committed.
"We take any allegations of electoral fraud very seriously and will continue to work closely with the Electoral Commission, and local authorities, to ensure we play our part to protect the integrity of the electoral process in Staffordshire."
Mr Nuttall lost the seat at the by-election on 23 February 2017 to Labour's Gareth Snell - picking up 5,233 to Mr Snell's 7,853 votes.
Mr Snell held his seat in the following general election.
Labour had claimed Mr Nuttall's use of an empty house as his address raised questions about his fitness for public office.
However, UKIP said Mr Nuttall had stayed overnight and was using it as a base while campaigning.
The Electoral Commission's guidance for candidates and agents states home addresses "must be completed in full" and "must be your current home address" but "does not need to be in the constituency in which you intend to stand".
Staffordshire Police said "considerable media interest" in the allegations had prompted an investigation.
Mr Nuttall stepped down from the party in June 2017 after its performance in the general election.