Seven British police forces have confirmed that they are investigating allegations of electoral fraud by the Conservative Party during the 2015 general election campaign. Some have applied to extend a limit of one year to begin such investigations in order to do so.

The probes relate to a Channel 4 News investigation into campaign spending by the Conservative Party during three key by-elections. The news show's researchers reportedly found about £200,000 ($288,610) of seemingly undeclared election expenses in 33 constituency elections carried out over 2014-2015. The broadcaster said the expenses should have been declared in the party's local spending returns.

Included in their calculations was £64,127 spent by the Tories on its Battlebus2015 tour, which transported activists to 29 key marginal seats in the final days of the campaign. The party was successful in 26. These costs included £38,201 for hotel bills, which were not declared by the Conservatives on either national or local spending returns, Channel 4 News said.

It followed January's revelation by the broadcaster that £19,151 was spent in South Thanet where Ukip leader Nigel Farage was standing. More than £17,000 of this was declared as "national" campaign expenses, despite workers appearing to be involved in local campaigning.

The figures also show that the following month, Tories collected more than £99,000 worth of hotel receipts during the 2014 by-elections in Newark, Clacton and Rochester & Strood, which were seemingly never declared. They found 770 bookings had been made using the name and/or address of a one Conservative Party campaign worker.

In a statement provided to the IB Times UK, a Conservative Party spokesman said that Conservative Campaign Headquarters had campaigned across the country.

"Such campaigning would be part of the national return, not local return, as the Electoral Commission has said," he said. "As is apparent from our National Return, the Party declared expenditure related to our CCHQ-organised Battlebus. However, due to administrative error, it omitted to declare the accommodation costs of those using the vehicles."

The spokesman added that the Tories had already brought this to the attention of the Electoral Commission, adding that the party had always taken the view that the Battlebus "was part of the national return and we would have no reason not to declare it as such, given that the Party was some millions below the national spending threshold".

Nonetheless, seven police forces have confirmed that they are currently investigating allegations relating to improper electoral expenses. They include Greater Manchester Police, Devon and Cornwall, Northamptonshire and Cheshire, as well as Staffordshire, West Yorkshire and Gloucestershire police forces.

In a statement Devon and Cornwall Police said it had met with representatives from the Electoral Commission and the Crown Prosecution Service.

While it was "fully aware that there is a 12-month limitation of proceedings for certain offences", which would run out in June 2016 it said investigators were "awaiting further guidance and legal advice in relation to the specific points relevant to election legislation".

While Gloucestershire Constabulary would not be drawn on which constituencies it was investigating, a spokeswoman confirmed the force had received an allegation of electoral fraud and was "considering an application for extension on time to investigate".

West Yorkshire Police meanwhile said they would be seeking an extension on the one-year time limit, as was Greater Manchester Police.