Businessman Sir Victor Blank has welcomed Ed Miliband's "sensible" pledge to offer voters an EU referendum if there is a proposed transfer of powers from Westminster to Brussels.
The former Lloyds TSB chairman expressed strong support for British membership of the EU, saying the prospect of an exit was "horrific".
One of Labour's biggest donors, John Mills, has said Ed Miliband's pledge to hold an EU referendum if there is a transfer of powers from Westminster to Brussels is "a step in the right direction".
However, Mr Mills has been clear that he would like Labour to promise an in/out referendum.
He said this morning: "I think we should recognise that the growth of the EU's influence over Britain in the past 40 years warrants a referendum regardless of future events."
David Cameron has hit out at Ed Miliband over his EU referendum pledge.
Speaking on a visit to Israel, the Prime Minister said only the Conservatives would offer the British people an in/out vote.
Ed Miliband drew laughs as he thanked ITV News' Deputy Political Editor Chris Ship's summary of Labour's "unclear" stance on an EU referendum after giving a speech on the issue at London Business School.
"I thought that was quite a good explanation", the Labour leader said, laughing.
ITV Deputy Political Editor Chris Ship has been tweeting from Ed Miliband's speech this morning on the European Union.
Ed Miliband ends his Q&A reaffirming his overall position: "We gain more not less from being part of the European Union"
The excesses of the EU include the "separate parliament building in Strasbourg" says Miliband
Miliband: what Cameron has done (pledged 2017 referendum) has "sent a chill down the spine of businesses round the world"
David Cameron has attacked Ed Miliband's EU referendum pledge, saying it makes "no sense whatsoever".
The Prime Minister told reporters on a flight to Israel: "It is not a proposal for an in/out referendum. It is a policy clearly designed by a committee who obviously couldn't agree what to do and have come up with a policy that makes no sense whatsoever."
He added: "It is absolutely clear - if you get Miliband, you don't get a referendum, you don't get a choice.
"It is the classic Labour 'we know best' approach to politics."
An in/out referendum on EU membership under a Labour government is "frankly unlikely", the shadow foreign secretary Douglas Alexander has said.
He said a vote was still "possible" if there was a transfer of powers from Westminster to Brussels.
ITV News Deputy Political Editor Chris Ship is at Ed Miliband's speech setting out Labour's position on an EU referendum:
So far: Miliband says we need to be IN European Union but it needs to change.
Well this bit is clear: tackling world problems more effective inside EU; UK stronger part of EU; economic case for membership overwhelming
Miliband: Cam's promises on Europe are "undefined, undeliverable and are now unravelling." <Might that also apply to Labour's new position?