Nigel Farage has warned Andy Burnham will tell voters one thing and Labour MPs another “as he positions himself for power”.

The Reform UK leader branded the Mayor of Greater Manchester “open-borders Burnham”, adding people “deserve honesty” in the upcoming Makerfield by-election.

He declared the Labour leadership rivals have given “the clearest signal yet” they are “preparing to completely betray Brexit voters.”

Former Health Secretary Wes Streeting on Saturday declared “Britain’s future lies with Europe”, while Mr Burnham told ITV there was a “long-term case” for rejoining the bloc.

But he will not make the case during the critical by-election on June 18, prompting fears of a deliberate deception.

Mr Farage told the Express: “For months, it has been clear that Keir Starmer has been attempting to sleepwalk us back towards the European institutions.

“But this weekend provided the clearest signal yet that Labour is preparing to completely betray Brexit voters.

“The upcoming contest in Makerfield will become a flashpoint in that battle. It is increasingly obvious that Andy Burnham wants to say one thing to Labour voters in the constituency while telling Labour MPs something entirely different as he positions himself for power.

“Voters are not fools and they deserve honesty from open-borders Burnham.

“Andy Burnham’s position raises serious questions. At a time when millions of voters are demanding control of our borders, he continues to advocate re-joining a European project built around the free movement of 500 million people.”

Mr Burnham’s supporters effectively want him to have a coronation, as Sir Keir Starmer flounders in Downing Street, desperately trying to cling on to power.

In a speech on Saturday, Mr Streeting called for the UK to rejoin the European Union, saying that “Britain’s future lies with Europe”.

The former health secretary branded Brexit a “catastrophic mistake”, adding that Britain needed a new “special relationship” with the trading bloc.

And Mr Burnham said: “I've said in the long-term there is a case for that, but I'm not advocating that in this by-election.

“In fact, what I am saying is focus now domestically, Britain has got to focus very much on the here and now and the issues that are affecting people.

“So one of the big ideas that, you know, I will be putting forward in this campaign is the re-industrialization of Britain, building future facing industries and bringing them to areas like Makerfield and then alongside that, reforming education so that the technical, so young people can follow a technical path and it can be equal to the university route.”

But Makerfield voted by 65% to leave the European Union in 2016.

And Mr Farage’s party won all eight of the council wards covering the majority of the area.

Reform UK will make a “Brexit betrayal” one of its key attack lines in the by-election campaign.

They could even print Mr Burnham's words on leaflets.

But interventions by Labour’s leadership hopefuls into Britain’s historic decision to quit the bloc sparked anger in the current Government.

Culture Secretary Lisa Nandy slammed Mr Streeting and Mr Burnham for reopening the “Brexit wars”.

She told Sky News’s Sunday Morning With Trevor Phillips: “The Government, that he was part of until recently, has been trying to take a far more pragmatic approach to bringing us closer to Europe and repairing some of the damage that was done from a poor Brexit deal to people’s living standards in parts of the country like mine, rather than reopening the Brexit wars and going round back again around that track.”

Ms Nandy added: “If rejoining the EU is the answer, then essentially what we’re saying to people is ‘life was fine in 2015, we just need to go back there’.

“I know Wes is coming up to campaign in the by-election quite soon. He will hear loud and clear from people in places like Wigan, Ashton, Winstanley, across Makerfield, that that is absolutely not the case. And the answer has to be bigger.”

Tory Kemi Badenoch said the row shows Labour does “not have a plan for this country”.

She told Sky News: “The country wants us to make the best of Brexit, make the best of leaving the EU.

“The idea of starting again, going backwards, having all of these negotiations, this is a sign of the Labour Party that does not have a plan for the country, so they want to go back and refight wars which were settled a long time ago. And I’m saying that we’re the only ones who have a plan.”

Leading Brexiteers are set to come together this week for a conference organised by the Freedom Association.

Sir Iain Duncan Smith will say at the meeting in London: “The Labour Party has no electoral mandate to override the biggest vote this country has ever seen when voting for Brexit.

“We must defend the overwhelming democratic vote of the British people and fight to make sure Brexit is not betrayed.

“The Labour Party’s internal leadership psycho-drama should hide the fact that they plan to take the UK back into the expensive clutches of the EU. In short, Labour wants to wreck Brexit.

“Yet there is no mandate for them to do so. They promised in the general election they would stand by the Brexit vote, and yet they now plan to break that promise and take us back into the EU. Every election since Brexit, the vast majority of voters backed parties that ruled out efforts to reverse Brexit.

“The British people will be forced to pay huge costs but will have no vote.

“Together we here today say, Starmer, stop this deceitful plan to take us back into the clutches of the EU and stand by your promise not to defy the vast majority of British people.”