Cumbria Police is one of a dozen forces to have sent files to prosecutors as part of a probe into the Conservatives' 2015 election expenses.
With police and the Electoral Commission investigating, Conservative Party chairman Sir Patrick McLoughlin has been urged to act to protect MPs who face accusations they breached local campaign spending limits.
At least three Tory MPs have been quizzed by police investigating whether election finance laws were broken in the 2015 contest.
And today, the Conservative Party has been fined £70,000 by the Electoral Commission for failing to accurately report its election expenses.
The independent elections watchdog said the party had made "numerous failures" in reporting its expenses for the 2015 General Election and three by-elections in 2014.
Commission chairman Sir John Holmes said the Tories' failure to follow the rules "undermined voters' confidence in our democratic processes" and said there was a risk political parties were seeing such fines as "a cost of doing business".
Tory MP Anne-Marie Trevelyan said she hoped the "very difficult" situation would be resolved "very quickly".
I think the whole situation is very difficult and I hope very much that it will be resolved this week.
Morecambe and Lunesdale MP David Morris is one of three MPs known to have been interviewed by police.
"Lancashire Police interviewed me and they saw fit not to take it any further," he said.
He said he did not want a visit from the battle bus campaign at the centre of many of the claims about election spending breaches.
The Conservatives have insisted that the busloads of activists sent to key seats formed part of the national campaign spend rather than falling within the lower constituency limits.
We were all given an email, every one of us had the same email from Mark Clarke at the time who was running the battle bus project, saying it was a national spend.
The disclosure follows reports that Craig Mackinlay, who fought off a challenge from former Ukip leader Nigel Farage to hold Thanet South for the Tories, had been questioned for six hours last week by Kent Police.
Colchester's Will Quince also revealed that he had been interviewed by police and told he faced no further action.
Mr Quince voluntarily attended an interview under caution with Essex Police last January.
Essex is not one of the forces that has submitted files to the CPS.
But a CPS spokesman said it had received files from: Avon & Somerset, Cumbria, Derbyshire, Devon & Cornwall, Gloucestershire, Greater Manchester, Lincolnshire, the Metropolitan Police, Northamptonshire, Nottinghamshire and West Yorkshire police.
Once it has received a file, the CPS will decide whether to charge anyone.
The files were "all under consideration", a spokesman said.
A 12th force - Staffordshire - said it had also sent a file to the CPS.