The man once described as Baroness Thatcher's favourite businessman has been lined up by the Labour peer Lord Hollick to front the "yes" campaign in a referendum on economic and monetary union.
Downing Street believes Lord Marshall - now a crossbench peer - will give credibility to the drive for the euro and help persuade business of the case for giving up the pound.
Colin Sharman, head of the accountants KPMG, is also likely to play a leading role in the campaign, "Britain in Europe".
The appointments are expected to be announced shortly, along with the membership of the all-party board of the group. Lord Sainsbury, the science minister, is among the Labour Party members who have already pledged money to the campaign.
Conservatives including Kenneth Clarke and Michael Heseltine have decided not to announce their support until after the European elections in June, but insiders say they have a "gentleman's agreement" that they will throw their weight behind the campaign after that.
Mr Heseltine will this week up the stakes in his battle with William Hague by making a barnstorming pro-European speech to the Conservative Party faithful. He has agreed to speak at a Conservative Mainstream fringe meeting at Tory Central Council next weekend."
"He has set himself up as the messiah leading the people from the wilderness to the promised land, that's the role he is going to be playing next weekend," one ally said. "He is certainly likely to deliver enough to make the point, and if provoked he could be extremely forceful about it."
Last week Mr Hague warned Mr Heseltine and Mr Clarke that they would be thrown out of the party if they supported the Pro-European Conservative Party in the European elections.Reuse content