The leader of Britain’s biggest trade union has urged Jeremy Corbyn not to support a second Scottish independence referendum in a potential pact with the SNP.

Len McCluskey, general secretary of the Labour-supporting Unite union, has previously said he would have voted for independence if he had lived in Scotland at the time of the 2014 referendum.

First Minister Nicola Sturgeon earlier this month told Labour leader Corbyn “don’t bother picking up the phone” without an independence referendum pledge.

But yesterday McCluskey said: “If I was Jeremy, I wouldn’t concede to a demand of that nature.”

But he called on the SNP to still back a Labour government if it was the biggest party after a general election.

“I think Labour as a minority government, not as a coalition government, would put forward a programme of social change, and I hope the SNP would support that.”

Unite had a neutral stance on Scottish independence during the 2014 referendum.

McCluskey said: “I believe the political arena has changed. I believe that when Corbyn was elected it changed British politics for ever.

“I don’t think we’ll ever go back to a position where ordinary people say ‘they’re all the same, they’re only in it for themselves’.”

McCluskey also described the prime minister’s Withdrawal Agreement Bill as a car where “half the engine has gone”.

He further warned hundreds of thousands of manufacturing jobs were at risk to appease “a handful of rabid right-wingers”.

McCluskey told delegates at a Unite Scotland conference in Ayr: “The Tories never miss a chance to exploit a crisis. They see this as their opportunity to reshape our nation as the North Sea’s low tax, no rights sweat shop – and they will grab it with both hands.

“That is why Mr Johnson does not want us peering too closely at his Withdrawal Agreement bill. Like a dodgy used car salesman, Johnson didn’t want us checking over the goods. He ignored calls for clarity on the economic impact of his deal. He tried to bounce his deal through parliament in 72 hours.

“The arrangement to end a 40-plus year relationship with our biggest trading partner is being given less consideration than the Act of Parliament that set out the regulations for handling salmon.

“And neither Holyrood nor the Welsh Assembly will be granted the time to assess proposals which will impact on the prosperity of their communities and the reach of their devolved powers.”

At the Unite conference in Ayr today, Labour leader Jeremy Corbyn will promise a Labour government would invest £70 billion in public services and infrastructure in Scotland.

He will also pledge to give 750,000 workers a pay rise, including £1,200 per year to those on an average hourly wage of £9.10. He will also vow to save more than 500,000 people in Scotland from the “indignity, suffering and misery” of Universal Credit by scrapping the welfare scheme.

Labour’s policy is to renegotiate a Brexit deal with the EU and put it to a public vote if it wins the next general election.

MPs are expected tomorrow to consider Boris Johnson’s call for an early general election.

The Prime Minister previously said he would rather be “dead in a ditch” than renege on his promise of Britain leaving the EU by October 31.

But after being blocked by Westminster last week, he has called for a general election on December 12, which would have to be backed by two-thirds of all 650 MPs.

The EU is this weekend considering whether to extend the Brexit deadline to January 31 or a shorter November delay.

It is concerned Britain may try to loosen regulations, including slashing workers’ rights, after Brexit.

Stephen Gethins, the SNP’s Europe spokesperson, said: “Despite all the rhetoric, it’s clear that Boris Johnson and his government are planning to rip up workers’ rights and pursue a post-Brexit race to the bottom on regulations that have maintained key protections for workers.”