Carlisle MP John Stevenson has been quizzed by police as part of a national probe into whether a dozen Conservative politicians broke expenses rules.

The politician was interviewed under caution about spending on his party's General Election “Battlebus” campaign in Carlisle – but he said he is confident he did not break the law.

Mr Stevenson is one of a dozen Conservative MPs potentially facing criminal charges, The Cumberland News can reveal

The news came as the Conservative Party was fined £70,000 for failing to accurately report on how much it spent on campaigning at three by-elections in 2014 and at the 2015 UK Parliamentary general election.

The ten-month police battlebus expenses investigation focused on whether the Conservative campaign, which took activists to key marginal constituencies, was illegally recorded as national spending.

All would-be MPs must stick to strict local and national spending limits designed to prevent the wealthy from having an unfair advantage.

Eleven police forces – including Cumbria – have now passed investigation files to the Crown Prosecution Service so that lawyers can consider whether or not charges should be brought against those involved.

Mr Stevenson told The Cumberland News there is clear evidence that the spending on his party's Battlebus visit to Carlisle was done in strict accordance to instructions from Conservative Party HQ.

He posed for photos with fellow Conservatives – including Penrith and the Border MP Rory Stewart - in front of the Battlebus when it visited the city on May 2, 2015.

“The question is did we knowingly submit false returns, and clearly we did not because we genuinely believed it was a national expense,” he said.

“I'm happy to cooperate with the police because in my view no offence was committed.”

Commentators suggest the potential consequences of the police probe if it does lead to prosecutions could be a declaration that Conservative victories in the constituencies involved could be declared void.

That would trigger a string of byelections.

Mr Stevenson clinched victory in Carlisle with a majority of 2,774 votes, beating Labour's candidate Lee Sherriff into second place.

In an earlier statement, Mr Stevenson said he did not believe his party had intentionally done anything wrong after it emerged party officials failed to declare £38,000 of general election expenses.

The party said an "administrative error" was behind its failure to register the accommodation costs of activists who followed a Conservative Battlebus during the 2015 general election campaign.

It visited a number of key marginal seats across the country, including Carlisle.

The Tories at the time insisted the Battlebus operation was part of their national campaign organised by its Conservative Campaign HQ and therefore the expenditure did not form part of the spending by individual candidates.

But an investigation suggested the operation was focused at a local level, so should have been declared as such.

The Crown Prosecution Service confirmed that it had received files from Avon & Somerset, Cumbria, Derbyshire, Devon & Cornwall, Gloucestershire, Greater Manchester, Lincolnshire, the Metropolitan, Northamptonshire, Nottinghamshire and West Yorkshire police forces.

A Cumbria Police spokesman said: “The constabulary can confirm that they have submitted a file to the Crown Prosecution Service in relation to party election expenses.

"Police have interviewed those connected with the party in question and are waiting the Crown Prosecution Service’s decision.”

A Conservative Party spokesman said that its Campaign HQ always took the view that its nationally directed battlebus campaign was part of its national return, and it had no reason not to declare it as such, given that the Party was £2m below the national spending threshold.

He said: “The Electoral Commission report makes clear that our interpretation of the guidance was correct, stating: ‘The Commission has found no evidence to suggest that the party had funded the Battlebus 2015 campaign with the intention that it would promote or procure the electoral success of candidates’.

“MPs in constituencies visited by the battlebus would have no reason to consider whether it should be included in their local return: they were directed that the bus would be visiting as part of CCHQ’s national spending.

“The ongoing investigations relate to national spending by CCHQ and the national party will continue to co-operate with the police and other authorities so that the matter can be resolved as soon as possible.”

The spokesman added: “The Conservative Party has complied fully with the Electoral Commission’s investigation since it began more than a year ago and will pay the fines they have imposed.

“This investigation and these fines relate to national spending by CCHQ, and the Conservative Party’s national spending return for the 2015 general election.

“As we have consistently said, the local agents of Conservative candidates correctly declared all local spending in the 2015 general election.

"CCHQ accepted in March 2016 that it had made an administrative error by not declaring a small amount constituting 0.6 per cent of our national spending in the 2015 election campaign.”

An Electoral Commission investigation concluded that the Conservative Party’s 2015 UK Parliamentary general election spending return was missing payments worth at least £104,765.

Separately, payments worth up to £118,124 were either not reported to the commission or were incorrectly reported.

The party also failed to maintain records explaining the amounts it invoiced to candidates in three 2014 byelections, for work on their campaigns. Therefore the accuracy of the amounts could not be verified.

Sir John Holmes, chairman of the Electoral Commission, said: “Our investigation uncovered numerous failures by a large, well-resourced and experienced party to ensure that accurate records of spending were maintained and that all of the party’s spending was reported correctly.

“The rules established by Parliament for political parties and their finances are there to ensure transparency and accountability.

“Where the rules are not followed, it undermines voters’ confidence in our democratic processes, which is why political parties need to take their responsibilities under the legislation seriously.”

The other Conservative MPs interviewed by police are reported to include Craig Mackinlay, the Tory MP for South Thanet, whose opponent in the General Election was Ukip Leader Nigel Farage.