The Electoral Commission is to investigate Cabinet minister Chris Huhne's election expenses.
The watchdog said it had started a case review after receiving an allegation regarding the Liberal Democrat Energy Secretary's 2010 general election expenses.
On Friday, the commission said there was insufficient evidence to substantiate a similar allegation made against Mr Huhne, who is also the subject of a police inquiry into claims that he dodged punishment for speeding.
An Electoral Commission spokesman said: "The commission received an allegation regarding Chris Huhne MP's 2010 general election expenses on May 25.
"Following an initial assessment of the information, we have now started a case review into the matter. The review will look to establish the facts of the case, firstly for the purposes of transparency and also for possible future guidance."
In a statement, Mr Huhne said: "I have full confidence that my agent has declared my election expenses correctly and I look forward to this complaint being rejected as roundly as the last one."
The complaint relates to alleged "irregularities" in the MP's declared election expenses. The Sunlight Centre for Open Politics said it had found evidence of a potential overspend.
Allegations Mr Huhne made a "false declaration" of his election expenses were referred to the Commission earlier this month by two former Liberal Democrat councillors in his Eastleigh constituency.
The allegation was based on a recording of a local party meeting where treasurer Anne Winstanley is heard saying that the elections "have cost more than we declared".
Mr Huhne and his ex-wife Vicky Pryce were interviewed by detectives last week over claims that he persuaded her to accept a penalty on his behalf in March 2003. Mr Huhne, who left Ms Pryce for another woman last year, denies the allegations.
