11 per cent would back third party, four per cent would vote Democrat

In total 34 per cent said they may not vote Republican at general election

With Ted Cruz's upset victory over Donald Trump in Wisconsin last week, talk of a contested Republican convention reached fever pitch as the math seemed to stack up against the frontrunner.

Even Trump himself seemed to sense the mood change as he brought Paul Manafort, an expert convention planner, into the ranks of his campaign team this week.

But if the GOP are intent of dethroning Trump at a contested convention, they may want to think again as a third of the billionaire's supporters say they would turn their back on the party afterward.

A poll of Republican Trump supporters has revealed that 34 per cent of them could fail to support the GOP at a general election if he wins the delegate count, but is denied the nomination

That figure includes 11 per cent who said they 'don't know' what they'd do if Trump is denied the party nod, while another four per cent say they would vote Democrat to spite the party

Reuters and IPSOS asked almost 500 of Trump's Republican backers what they would do if Trump topped the delegate count, but did not get the nomination.

While 66 per cent of people said they would still vote for the party at a general election, 34 per cent were open to the idea of abandoning the GOP in the eventual contest.

Of those, 11 per cent said they 'did not know' what they would do if Trump were robbed of the nomination, while another 11 per cent said they would support a third-party candidate.

Six per cent of that group said they would not vote in the general election, while four per cent said they would back the Democrats in order to spite the Republicans.

Elizabeth Oerther, 40, a Trump supporter from Louisville, Kentucky, said: 'If you don't give it to him, I'm going to vote against them. They want to take away the choice of the people. That's wrong.'

Worryingly for senior GOP figures, 16 per cent of those polled said they would leave the Republican party altogether if the nomination is stolen from under Trump.

Chuck Thompson, 66, a Trump supporter from Concord, North Carolina, added: 'If they broker him out, I'll be fed up with the Republicans.

'The people want Donald Trump. If they can't deal with that, I don't need them.'

Worryingly 16 per cent of Trump supporters say they would leave the Republican party altogether if Trump does not get the nomination, a potentially devastating blow in a general election

'Never Trump' campaigners, whose hopes rest on Ted Cruz , are now faced with the possibility of nominating Trump, which they believe will hurt the party, or denying him the nomination, which would have the same effect

Donald Green, an expert on election turnout at Columbia University, said: 'If it's a close election, this is devastating news.'

He added that the departure of even a small number of Republicans would make it tough for the party to prevent the Democrats from winning the White House, especially if the election is again decided by razor-thin margins in a handful of battleground states.

Meanwhile Trump has spoken of 'riots' among his supporters if the nomination is taken away from him, a statement seen by his critics as a veiled threat.

Still, the polling suggests the so-called 'Never Trump' movement has found itself stuck between a rock and a hard place.