Eight police forces have launched investigations into an allegation of electoral fraud relating to the 2015 general election, amid claims the Conservative Party broke electoral spending rules.

The party faces claims it failed to record accommodation costs for bussing activists to key constituencies as part of candidates' spending, instead recording them as part of national campaign spending.

Up to 29 Conservative candidates are thought to have benifitted from the Tory "Battlebus" campaigns.

General election 2015: Polling day Show all 16 1 /16 General election 2015: Polling day General election 2015: Polling day General election 2015 Nuns arrive to vote at a polling station at St John's Church in Paddington, London General election 2015: Polling day General election 2015 A voter leaves the White Horse Inn in Priors Dean, also known as the 'Pub with no name', which is part of the East Hampshire constituency and acts as a local polling station on the day of the election General election 2015: Polling day General election 2015 General view of inside the White Horse Inn in Priors Dean General election 2015: Polling day General election 2015 People cast their votes as a man uses a punch bag in the East Hull Boxing Academy, which is being used as a polling station in Hull General election 2015: Polling day General election 2015 Penny Higbee waits to greet voters at her home in Routh, East Yorkshire, which is being used as a rural polling station General election 2015: Polling day General election 2015 Voters in Ironbridge, Shropshire, arrive to cast their vote at The Iron Bridge Tollhouse General election 2015: Polling day General election 2015 A voter arrives at the North West Ambulance Service Station at Milton Green, Cheshire, which is being used as a polling station as Britain goes to the ballot box General election 2015: Polling day General election 2015 A polling station has been installed in a launderette in Oxford General election 2015: Polling day General election 2015 SNP candidate for the Gordon constituency and Former First Minister Alex Salmond with first time voter Nicki Falconer, and her family, (L-R) Mackenzie, Nicki, Skye, Alex Salmond and Keiran at their local polling station in the Gordon constituency in Ellon, Scotland General election 2015: Polling day General election 2015 Prime Minister David Cameron and wife Samantha after casting their votes at Spelsbury Memorial Hall, Witney General election 2015: Polling day General election 2015 Liberal Democrat leader and Deputy Prime Minister Nick Clegg and his wife Miriam Gonzalez Durantez arrive at Hall Park Hill Community Centre to cast their votes, in Sheffield General election 2015: Polling day General election 2015 Labour Party leader Ed Miliband and his wife Justine Thornton leave the polling station at Sutton Village Hall in Sutton after casting their votes in the 2015 general election in Doncaster General election 2015: Polling day General election 2015 First Minister of Scotland and leader of the SNP Nicola Sturgeon, votes with her husband Peter Murrell in Glasgow, Scotland General election 2015: Polling day General election 2015 Ukip leader Nigel Farage arrives to cast his vote for the South Thanet constituency in Ramsgate General election 2015: Polling day General election 2015 Plaid Cymru leader Leanne Wood arrives at a polling station in Penygraig, Rhondda, Wales General election 2015: Polling day General election 2015 Green Party leader Natalie Bennett after casting her vote at Ossulston Tenants' Hall, London

A series of police forces have said they will launch investigations into the allegations, including Gloucestershire Police, Devon and Cornwall Police, Cheshire Police and West Yorkshire police.

Derbyshire Police, Greater Manchester Police, Northamptonshire Police and Staffordshire Police are also actively investigating allegations, the BBC reported.

The BBC also reports a further four forces are awaiting further information.

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The investigation comes after the Electoral Commission met with police and prosecutors on Wednesday to ensure they did not run out of time to launch possible criminal investigations into the Conservative's 2015 general election campaign funding.

The Commission believes its ongoing probe into alleged breaches of reporting obligations will take at least another month - potentially taking it past the one-year time limit for launching criminal proceedings.

Tory anti-corruption "tsar" Sir Eric Pickles, a former party chairman, said the Conservatives were confident everything during the 2015 election was "above board" and said he had "complete confidence" in the team who organised the submission of expenses.

"I'm told that the party is confident that it will be able to successfully demonstrate that everything was above board but I have no inside knowledge inside the party on this," the former Cabinet minister told BBC Radio 4's The World At One.

"These are matters that are quite normal in politics, I don't have any inside knowledge, I don't know, I haven't seen how the forms were filled in, but I know the people that did this and they are very professional and I've got complete confidence in them."