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Police investigating claims that more than 20 Tory MPs failed to fully declare their general election spending are holding crunch talks with officials from the Electoral Commission and the Crown Prosecution Service next week, the Mirror can reveal.

Up to 29 Conservative candidates are alleged to have benefitted from the notorious Tory Battlebuses but failed to declare the costs of hiring the buses or putting hundreds of volunteers up in hotels.

When the Mirror first revealed the claims in March, the Conservatives insisted that all Battlebus costs were fully reported in the party's national spending returns.

But it has since admitted , following a Channel 4 News investigation, that £38,000 in hotel bills were not included due to an "administrative error". This is being investigated by the Electoral Commission.

(Image: @Roadtrip2020/Twitter)

Now officers in 15 police forces around the country are investigating complaints that some or all of the costs should have been included in the local spending returns of the individual candidates.

At least 20 of the winning Tory MPs may have broken strict local spending limits which, if proven, could lead to calls for by-elections. It is a criminal offence under the Representation of the People Act for candidates and their election agents to fail to declare election spending. The maximum penalty is one year in jail or an unlimited fine.

West Midlands Police are leading the investigation and a source told the Mirror: "These claims are being taken very seriously."

Read more:Did the Tories 'break election laws' with battle bus spending? Here's everything you need to know

The Devon and Cornwall Police force covers at least three constituencies visited by the Roadtrip2015 Battlebuses – Plymouth South and Devonport, Torbay and North Cornwall. The force told the Mirror it has received “a number of complaints” and its “inquiries are ongoing”.

A spokesman said: “Devon and Cornwall Police, plus representatives from other forces in which constituencies are believed to have been effected, have been invited to a meeting in relation to the Election Expenses of the Conservatives Party, along with representatives from the Electoral Commission and the CPS.

“Details surrounding this meeting including the date and location are still to be confirmed.”