Prosecutors are deciding whether to pursue criminal proceedings against Farming Minister George Eustice after he was caught up in the Conservative election expenses scandal.
The party’s 2015 election campaign saw large groups of volunteers bussed into key marginal seats, such as Mr Eustice’s Camborne, Redruth and Hayle constituency, which he won in 2010 with just 66 votes.
The fact that associated costs were claimed as a national expense – even though the volunteers were promoting local candidates – has been seen as a breach of election rules which put a cap on spending.
A spokesman for Mr Eustice told the Plymouth Herald: “Every constituency in the country known to have been visited by volunteers as part of the national battle bus campaign is being reviewed by the police.
“A group of unpaid national volunteers who travelled to Cornwall by bus spent about an hour in Hayle during the last election and the costs associated with the bus were a national campaign expense.
“George provided the police with all the information they requested several months ago.”
There are up to 20 other MPs under investigation, including Craig Mackinlay, who stood against former UKIP leader Nigel Farage in South Thanet.