Conservatives must not ignore Europe in their leadership debate, deputy party leader Michael Ancram has said.
Michael Ancram says the next leader must 'stand up for Britain'
The warning made in a speech to his local party is likely to be seen as an attempt to counter the challenge of pro-Europe candidate Ken Clarke.
A BBC Newsnight poll suggests Mr Clarke is four times more popular with ordinary voters than his nearest rival.
Meanwhile, fellow hopeful Sir Malcolm Rifkind will start a tour of the UK in Derbyshire to try to boost his chances.
In his speech to his constituency of Devizes, Wiltshire, Eurosceptic Mr Ancram called for the selection of a leader who would "stand up for Britain".
Mr Clarke is widely believed to have lost out on the job of leader in 1997 and 2001 because the party's grassroots activists opposed his pro-Europe standpoint.
The issue of Europe could not be "swept under the carpet", Mr Ancram said.
"If the outcome of the Conservative leadership contest is to be positive, it can't just be based on personalities - we need a comprehensive debate on the issues," he argued.
"I therefore find it quite astonishing that, so far, Europe appears to have been marked 'not for immediate discussion' and sidelined."
The party needed a leader to "stand up for Britain" rather than being "fobbed off by Euro-flattery", said Mr Ancram.
And he repeated a call to renegotiate existing EU treaties to stop the "surrender" of sovereignty to Brussels.
The Newsnight poll, revealed on Monday night, suggests 20% of people would be more likely to vote Tory with Mr Clarke as leader, and 8% less likely.
Of the ICM Research random sample of 1,007 adults aged over 18, 40% said Mr Clarke would make the best leader, compared with 10% for David Davis and 4% for David Cameron and Malcolm Rifkind.
Sir Malcolm will try to boost his campaign on Tuesday when he begins a 12-day tour of the country meeting activists in areas with little Tory representation.
There must not be any "no-go areas" for Conservatives, he said.
As well as Derbyshire, he will also make speeches and visit activists in London, Edinburgh, Ayr, Cardiff, Swansea, Wakefield, Birmingham, Manchester, Liverpool, Nottingham Leicestershire, Bath, Newcastle and Croydon ahead of next month's annual conference.