Who is best placed to unite the Conservative Party?

Clarke - 46% Duncan Smith - 20% Source: Mori

But a separate, small scale poll suggests his rival Iain Duncan Smith has the crucial advantage among the electorate that matters - paid-up members of the party.

After attending a private hustings meeting in London on Wednesday, both candidates are heading to Scotland over the next two days to woo the votes of the 20,000 Tories north of the border.

The Mori poll for the Times showed a narrow majority of ordinary people believe Mr Clarke is the best candidate to unite Tories despite his support for the single European currency.

Top job

He was backed by 46% of those questioned, while just 20% favoured the right-wing shadow defence secretary.

And 48% of Conservative voters want Mr Clarke as leader, compared with 35% who say Mr Duncan Smith should take the top job.

Who do Tory voters want to lead the party?

Clarke - 48% Duncan Smith - 35% Source - Mori

He was also seen as the unity candidate, with 39% saying he would bring the party back together while 36% said Mr Duncan Smith could heal the rifts.

And 56% of Tory supporters said Mr Clarke would increase the party's appeal against 30% who said the shadow defence secretary would make them more popular.

In a separate survey of 100 party members in Cambridgeshire north east, Mr Duncan Smith was ahead by three votes to one.

But there was bad news for whoever succeeds William Hague as leader.

Effective opposition

The protracted contest appears to have damaged the party's credibility, with 40% of voters saying the Liberal Democrats provided the most effective opposition, compared with 34% who said the Conservatives were doing the best job.

Mr Duncan Smith: poll suggests he is ahead among party members

The findings of the Mori poll, which questioned 2,084 adults between July 19 and 23, came after the candidates took to the hustings together.

The pair spoke to and took questions from activists at the Conservative Party's National Convention in Church House, Westminster, on Tuesday.

Behind closed doors, Mr Clarke told around 250 convention delegates the party must become "less dogmatic" if it was to again become an electoral force.

"We must retreat from moving out even further into our political factions and create a broader-based support for the Conservative Party," he said.

There was a need to encourage more women and ethnic minorities and people from wider backgrounds back into the party and into the parliamentary party, he also said.

Mr Duncan Smith outlined his agenda for regaining the common ground.

Broad appeal

The shadow defence secretary said his experience in the army and in industry made him appreciate that the party must appeal to a broad cross-section of British people.

The party needed to move on so that it better connected with the country it sought to govern, he added, which included encouraging greater participation of women, people from ethnic minorities and young people.

On Europe, he said his policy of "clarity with tolerance" would ensure that it became a positive issue for the party.