Shock for Romney as Right backs his rival

The anti-abortion, anti-gay rights candidate sent front-runner Mitt Romney's campaign into a spin after winning in Minnesota, Missouri and Colorado.

Although Mr Santorum won the first caucus in Iowa his campaign had stuttered while Newt Gingrich and Mr Romney set the early pace.

But analysts believe the influential conservative arm of the party is not satisfied with Mr Gingrich or Mr Romney and wants a more hardline candidate. Mr Romney, who currently leads the race to take on Barack Obama in November, was confident of victory when the polls opened, even planning a winner's speech in Denver.

As the results came in he delivered the speech, but with a less triumphant tone: "This was a good night for Rick Santorum. But I expect to become the nominee with your help."

Former White House adviser David Gergen was more damning, claiming: "The Romney bandwagon just went in the ditch."

Mr Santorum, a former Pennsylvania senator, told supporters: "I don't stand here to be the conservative alternative to Mitt Romney. I stand here as the conservative alternative to Barack Obama."

Almost as important as securing delegates' votes was the financial boost the victories provided for Mr Santorum's campaign - his camp's bank balance was almost empty.

His advisers have been keen to steer the campaign further to the Right to appeal to the heartland Republicans who swept George Bush to eight years in the White House. But Mr Romney remains firm favourite by virtue of his superior organisation and fund-raising.

However there is clearly concern among rank-and-file Republicans who have not warmed to him and are willing to try alternatives.