GETTY David Cameron urged the party to remain neutral during the campaign

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The party's top brass has decided to remain neutral in the run-up to the referendum, costing the 'in' campaign as much as £7million in lost funding. Remaining impartial will also mean the party will not disclose its coveted list of activists' contact details, which would be a goldmine for campaigners seeking to influence the vote either way. Any Conservative Party staff wanting to work for either side will only be allowed to in their own time.

Mr Cameron's desire to keep Britain a member of the EU is Westminster's worst kept secret, despite the Prime Minister saying anything is possible ahead of crunch renegotiation talks with Brussels. But the PM himself urged the party to remain unbiased during the campaign in a bid to remove any doubt of unfair influence over the final result. The party machine will now be prevented from petitioning for either side and Tory constituency associations will also be barred from providing resources. The party said it had "unanimously agreed to follow the recommendation of the Prime Minister that Conservative Party Headquarters (CCHQ) and the Party remain neutral during the upcoming EU referendum campaign".

It added: "CCHQ will not supply funds or voter information to either campaign. "CCHQ will permit its staff to work for either side in their own time, or by taking unpaid leave of absence. "Those who take unpaid leave will be able to return to their paid employment at the end of the campaign." Lord Feldman, the party's chairman, said: "I am delighted the Party Board has followed the Prime Minister's recommendation that CCHQ and the Party's Associations remain neutral in the EU referendum campaign. "The important thing is that the Party is able to come together and unite whatever the outcome." Steve Baker, a backbench MP and founder of the Conservatives for Britain campaign, said: "I am delighted the Prime Minister and the Party Board have decided that Conservative Campaign Headquarters, its data and funds will remain neutral in the forthcoming referendum. "There is a range of views within the Party about the EU, with many members waiting to see the deal before choosing how to campaign."

Dominic Cummings, involved in the 'out' campaign, added: "Conservative donors and activists we have spoken to strongly oppose money and data gathered by the official party machine being made available... "The party machine should be neutral and there should be strict controls to prevent either side accessing databases." The development is the latest set back for the pro-EU lobby, following changes to the wording of the referendum question. At the beginning of September, Mr Cameron agreed to change the precise phrasing on the ballot after the Electoral Commission deemed it to be biased in favour of the 'in' campaign.