A Labour eurosceptic should lead the "out" campaign at the EU referendum, the party's biggest donor has said.
John Mills, the founder of JML, said that Ukip leader Nigel Farage would put many potential backers off, and suggested ex-minister Kate Hoey as a suitable candidate, as well as Labour backbenchers Graham Stringer and Kelvin Hopkins.
Mr Mills, a vocal critic of Brussels, said that "a successful no campaign has to be a cross-party campaign".
"If it is all the Conservative Party and no Labour then it is never going to gel so it is really important to have key Labour figures in it," he said.
He admitted he would still vote to stay if David Cameron could secure sufficient reforms.
A leading independent employers' organisation has called for the Prime Minister to be "ambitious with business".
The Confederation of British Industry urged the new Government to set out clear plans for the country's economic growth and to take action within the first 100 days.
It said that business will take an active role in "arguing the case for the UK to remain inside a reformed EU" and argued that it is "vital" for the Government to set the bar for that EU reform at an "ambitious and achievable" level.
The new Government must get into its stride quickly. It should set out clear plans for the next parliament within the first 100 days, and have a laser-like focus on delivery.
The Prime Minister should prioritise building on the progress made to get the deficit down, finding more innovative ways to deliver public services and backing the final decision from the Airports Commission so we get diggers in the ground by 2020.
The Liberal Democrats will not rule out a referendum on staying in the European Union, Nick Clegg has confirmed.
"I am not going to draw a red line against having a referendum," the Deputy Prime Minister told Reuters.
His comments echo those he made during an appearance on ITV's The Agenda on Monday, he was asked if the EU referendum was a "red line" for the Liberal Democrats.
"I think we should have a referendum when we have to give away new powers to the European Union," Mr Clegg told the show.
David Cameron has said that a referendum would be a dealbreaker in any potential coalition tie-up, while the pro-European Liberal Democrats have resisted discussing the issue until this week.
Clegg strived to point out that he would not change his party's EU policy so close to the election, but his vocal stance on the issue this week suggests that he is open to a deal.
The consequences if you take a wrong turn could at its worst - and I'm not predicting this - mean that within a matter of years, two unions which are pivotal to the prosperity and way of life of everybody in Britain are lost.
"To be pro-European doesn't mean one is fearful of the British people," Mr Clegg added. "There are some circumstances in which a referendum should take place and I have always felt that.
EU migrants living in Britain should not be allowed to vote in a referendum on Europe, Nigel Farage has said.
Speaking on The Andrew Marr Show, the Ukip leader said his party could go into coalition with the Conservatives, as long as they offered an immediate referendum on EU membership under specific terms.
Speaking on BBC's The Andrew Marr Show, he said: "At the moment, there are four million or so EU citizens living in Britain that I do not think should be allowed to vote in that referendum."
During the interview, Farage also said his party would spend an additional £3 billion on frontline NHS services - using part of the £10 billion Ukip says it save by withdrawing from the EU.
The party says it also force migrants and tourists to pay for health insurance as a condition of entry, which it claims will save £2 billion of "wasted" money on "health tourism".
Bob Neil, Tory MP for Bromley and Chislehurst, has confirmed he will make another bid for an in-out EU referendum in law after coming third in the annual private member's bill ballot.
The former minister was the highest placed Conservative MP drawn at random, with Liberal Democrats Andrew George and Michael Moore securing first and second place.
Mr Neill, a strong supporter of the EU Referendum Bill, said: "One of the first votes I ever cast was on EU membership in the 1970s .Now as I pick up my bus pass I am getting the chance to work with colleagues to secure a referendum for the British people."
"Britain needs a new deal with Europe and the Conservatives have a plan for change in Europe - renegotiate, reform and put the deal to the British people in an in-out referendum by the end of 2017," he added.
David Cameron has said he is ready to invoke the Parliament Act to force through referendum legislation, after a previous bill introduced by Stockton MP Mr Wharton collapsed in January due to Labour and Lib Dem opposition in the Lords.
Downing Street has refused to wade into a row over the decision to potentially elect former Luxembourg premier Jean-Claude Juncker, after reports emerged that David Cameron warned Britain could leave the EU.
We are not commenting on this. It was a private meeting, a private conversation.
EU leaders should not bow to pressure from the minority in their decision of who to elect as European Commission chief, Jean-Claude Juncker has said, according to an advance extract of an article published in Germany's Bild am Sonntag newspaper on Sunday.
"Europe must not allow itself to be blackmailed," Luxembourg's ex-premier said, adding that a broad majority of Christian Democratic and socialist leaders in the European Council backed him.
He said he was in favour of getting "all of the other heads of government on board too" in the coming three to four weeks, and offered to hold talks on priorities for the next Commission.
German magazine Spiegel said David Cameron has warned German Chancellor Angela Merkel he may have to bring the UK referendum on EU membership forward if Jean-Claude Juncker becomes the European Commission chief.
The Prime Minister said he sees Mr Jucker, Mrs Merkel's candidate for the post, as too federalist and likely to damage his hopes of reforming Britain's EU ties.