David Mundell questioned by police over expenses
Mr Mundell met officers from Dumfries and Galloway Constabulary on Monday, the force confirmed.
A member of the public contacted police over the alleged breach in his general election campaign spending.
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Hide AdIt emerged in July that a 681 bill for a campaign advertisement had been omitted from the cost of his campaign and listed with an earlier period instead.
Had it been listed with the latter campaign, it would have pushed the cost over the limit by 466.
If established, it would mean the Dumfriesshire, Clydesdale and Tweeddale Conservative MP - who increased his majority at the election -exceeded the permitted limit, which is punishable by a fine.
A force spokesman said an investigation was under way and a report
would be sent to the procurator fiscal.
Mr Mundell has faced calls to step aside from his role in ensuring the good conduct of elections in Scotland until any investigation concludes.
The Conservative Party previously said Mr Mundell had not intentionally breached any rules and referred the matter to the Electoral Commission himself.