The controversial former minister Michael Mates is being investigated by police for alleged electoral fraud over his attempt to become one of the country's first police and crime commissioners.
A rival candidate accused Mr Mates, 78, of lying about his address on official forms in order to run for the £85,000-a-year job in Hampshire.
Thames Valley police confirmed last night that it had started an inquiry and anticipated completing it before voters go to the polls on 15 November to elect commissioners for 41 forces in England and Wales in one of the flagship Tory policies on law and order.
Electoral reform campaigners have warned that turnout could be lower than 20 per cent for the vote, which will create watchdogs with powers to hire and fire chief constables.
The investigation is the latest problem for the campaign of Mr Mates, one of the most high-profile figures to stand in the elections. He faced demands from within his own party to step down over money he received for giving up a rented flat in London.
He was also forced to respond to questions about his links with the disgraced businessman Asil Nadir, who was jailed this year for stealing from his own multinational company after returning to Britain from self-imposed exile in Northern Cyprus.
Mr Mates, the former Minister for Northern Ireland, was forced to resign in 1993 after presenting Nadir with a watch inscribed with "Don't let the buggers get you down" after the businessman's belongings were seized by the Serious Fraud Office. Mr Mates gave evidence at the trial at which Nadir was found guilty and jailed for a decade.
Don Jerrard, a former lawyer and candidate in the Hampshire crime commissioner election, wrote to the chief constable last month to request a fraud investigation into Mr Mates.
Mr Jerrard said Mr Mates used a flat in Winchester as an address of convenience when he lived in a substantial property in West Sussex. Mr Mates last night he was the innocent victim of a smear attempt. He said: "These allegations are completely untrue"