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A seventeenth police force has asked for more time to investigate alleged Tory election expenses fraud.

Cumbria Police have become the latest force to ask for the extension to look into the declared spending in the run up to last year's General Election.

Under election law, police have just one year to bring prosecutions for failing to fully declare expenses but may apply for more time.

Cumbria join West Yorkshire Police, Derbyshire Police, Greater Manchester Police, Warwickshire Police, Gloucestershire Police, Northamptonshire Police, Staffordshire Police, Cheshire Police, Kent Police, Metropolitan Police, Nottinghamshire Police, Wiltshire Police, West Midlands Police, Avon & Somerset Police, Lancashire Police in asking for the extension.

Devon and Cornwall Police have already been granted more time to look into the electoral expenses of four MPs and newly elected PCC Alison Hernandez who will be investigated by West Mercia police rather than her own force.

It is understood that 30 or more sitting Conservative MPs are involved, and some unsuccessful Conservative candidates.

The Daily Mirror broke the story in March that 23 MPs benefited from Battlebuses but did not declare costs locally.

This week we launched the People's Electoral Commission asking you to help us investigate alleged Tory electoral fraud.

We aim to publish online the electoral spending returns of every one of this Government's 330 MPs for the country to judge whether they were entirely truthful about their spending.

On the back of our story, there are now 17 police forces investigating these allegations and any MPs found guilty face up to a year in jail.

This could be the tip of the iceberg but time is running out for police to investigate . The authorities have just one year from the date the spending return was filed to launch an investigation and by June 11 it will be too late.

(Image: Getty)

Prime Minister David Cameron's Government has a wafer thin majority of 12 MPs and so just six by-elections could topple his regime.

Do you live in a constituency with a Tory MP? Use our widget to #checkatory today:

Search for your local Tory MP by postcode. If we have that MP's spending return, then you can read through it and tell us if you think anything is missing. Here are some hints on what to look for . If we don't have the paperwork, then please consider volunteering to get it for us .

Under current rules, election spending returns are not published online. Instead they are held by returning officers in council offices and only made available for inspection on request. This is outdated and should change.

Another anomaly is that the expert body in these spending rules – the real Electoral Commission - is in charge of national spending by political parties but has no power to investigate spending by individual candidates. That is currently a job for the police.

It has been asking Mr Cameron for new powers since 2013 but his Government has not replied.

Bob Posner, Directory of Party and Election Finance said: “The law currently stops short of giving the Commission the power to enforce candidates' spending rules and only the police can investigate if there's a problem. It's time to end that anomaly and give us the power to investigate and sanction.”