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."