The Crown Prosecution Service has received files from at least 12 police forces relating to general election expenses in 2015.
The investigation is looking into whether some Tory MPs overspent on their local campaigns, where there are strict spending limits that cannot be breached.
A CPS spokesman said it had received files from: Avon & Somerset, Cumbria, Derbyshire, Devon & Cornwall, Gloucestershire, Greater Manchester, Lincolnshire, the Metropolitan Police, Northamptonshire, Nottinghamshire, Staffordshire and West Yorkshire police.
Colchester's Will Quince revealed that he had been interviewed by police - the second Tory MP known to have been quizzed by officers investigating election expenses.
Mr Quince said he had been told by Essex Police he faced no further action after voluntarily attending an interview under caution last January.
In a statement posted on his Twitter feed, Mr Quince welcomed the decision by Essex Police but said the complaint against him had been "vexatious and politically motivated".
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.
There is growing anger among Conservative MPs still facing investigation by the police and the Electoral Commission in relation to spending during the 2015 election.
The allegations centre on the use of the Tory "battle bus" during the election campaign to visit key seats.
The probe is looking into whether expenses by individual Conservative candidates were incorrectly registered under the national campaign budget, which is much larger rather than counting towards individual candidates' spending limits.