SCOTTISH Labour sounds like a “party of middle class protest” and could slump to fourth place behind the Greens, according to one of the country’s most senior trade unionists.

Gary Smith, the combative leader of the GMB union north of the border, also complained that the party under Kezia Dugdale’s leadership had “nothing” to say on the constitution.

He also called for Labour to rule out any town hall coalition deals with the Tories after next year’s council elections.

In a historic defeat, Scottish Labour came third at May’s Holyrood election after winning its lowest share of the vote in decades.

Dugdale has since been at odds with her deputy Alex Rowley over strategy, particularly on the constitution where he believes Labour should back home rule rather than just opposing independence.

The GMB is a major Labour donor and has around 56,000 members north of the border, many of whom work in the defence and energy sectors.

Smith, who recently became GMB Scotland Secretary and who sits on the party’s governing Executive, believes the political class in Scotland has become disconnected from working class people.

On Donald Trump’s victory against Hillary Clinton, he said: “Trump had some very simple, compelling messages to working class people in America and workers who previously had voted for Obama.

“He said to the car workers, ‘[we are] not going to allow your employer to export your jobs’. He said to communities that had been hard hit by the American free trade agreement, ‘we are going to bring your jobs back’. "

Asked about the lessons Scotland’s political parties could learn from Trump, he criticised the SNP Government's record in office, but his assessment of Scottish Labour was scathing.

“I have said this to the Labour party - too often they sound like a party of middle class protest. They certainly don’t sound like a party that is seeking power.

“We look at the party’s position on Trident, on building defence ships or on energy, [Scottish Labour opposes Trident and fracking] they just don’t sound credible and they don’t sound in touch with working class people or communities.”

On the constitution, he is closer to Rowley than Dugdale: “The fact that Labour has got nothing to say on the constitution is going to hold them back. There’s no doubt about that.”

Asked about the upcoming local government elections, where Labour is expecting heavy losses, Smith said:

“If the fall-back position for Labour councillors is that they are going to try and retain their committee seats, or their position in power, by doing deals with the Tories, it will be an absolute disaster.

“We are 100% committed as GMB Scotland to say to the Labour party: there should be no pacts with the Tories after May.

“It would be better to sit having a period in opposition, take your medicine from the people, and re-group, rather than being lined up with the Tories, just trying to secure an extra few bob in expenses.”

He said it would be “absolutely shameful” for Labour councillors to enter into pacts with the Conservatives and said: “People will not forgive them for that.”

His call for no Tory deals will be controversial for some party figures who believe Labour should be appealing to voters who defected to the Conservatives in May.

Asked if he felt Scottish Labour had hit rock bottom, he said the frustration felt by some pro-independence voters with the SNP was a threat to Labour.

“You will have elements of the SNP that will go to the Greens. And there’s the real prospect, if Labour doesn’t get its act together, they will end up fourth in Scotland. And I have told them that.”

On the SNP, Smith said “well off” Scots were an element of the independence vote, adding: “Also part of the SNP’s coalition is just angry white men, and if they were down south, they would be UKIP.”

He also said a large number of poorer Scots voted for Brexit because of immigration: “The idea that Scotland is this idyll where migrant communities can move and they will be embraced, and we are all Jock Tamson’s bairns, is utter drivel.”

A Scottish Labour spokesperson said: "Labour is the only party in Scotland who stand for what the majority of Scots want - a strong Scottish Parliament inside the UK with close links to Europe. We are the only major party willing to use the new tax powers to invest in public services rather than carrying on the cuts. While the SNP and Tories spent the weekend obsessing about the constitution, Labour focused on defending communities against Tory and SNP cuts to our public services like the NHS, and for a rail fare freeze."