As nominations closed with five candidates in the race, Mr Redwood said he would stop the civil war in the Tory party by imposing a clear policy to rule out British entry into the single currency.
"If they wish to be in the Shadow Cabinet, and I think Ken should be in the Shadow Cabinet, then they will be required to stick to the Shadow Cabinet line.
"I say it must be settled now in this leadership election. The party must make up its mind in a few days' time. If Ken and others say that keeping up a campaign for a single currency of some sort is more important than being in the Shadow Cabinet, I will respect that position."
Mr Redwood said his clear rejection of a single currency was the only way to stop the Tory party having "all the charm of a Balkan battlefield". But his critics said it would deepen the splits in the party.
Mr Clarke's camp are hoping to take more than 50 votes in the the first ballot next Tuesday and there has been continued speculation that some could leave the party if it swung decisively towards Euro-scepticism.
Mr Redwood's move to turn the leadership election into a ballot on the European policy was intended to outflank the other right-wing candidates. William Hague issued a glossy brochure which did not mention the issue.
In the jockeying for position, Mr Hague claimed more support among the new intake, including the former Asda boss, Archie Norman. Michael Howard recruited David Faber, one of the backers of Stephen Dorrell who dropped out in favour of Mr Clarke.
Some of Mr Hague's supporters, who might have been thought to have been natural Clarke backers, were saying yesterday that the former Chancellor could not unite the party, which is why they had opted for Mr Hague. It was also being said at Westminster by Clarke supporters that Mr Clarke would gain a considerable push from the results of the constituency ballot.
On the right, the contest is still close between Mr Howard and Mr Lilley but Howard's supporters were saying they had made strong advances. Mr Redwood's supporters admitted Mr Howard's votes were holding up better than they had hoped.
However, Mr Hague distanced himself from Mr Clarke with proposers and sponsors from the right. With no outright winner expected next week, the outcome will depend on how the second preference votes break down in the second ballot on 17 June.