Scotland’s only Labour MP Ian Murray will defy his party leader and vote against triggering the formal process to leave the European Union, the Herald understands.

The challenge to his authority will come as an embarrassment to Jeremy Corbyn, who is due in Scotland later today.

The Labour leader has suggested that he will order his MPs to vote for Article 50 of the Lisbon treaty, starting the clock ticking on a two-year deadline towards Brexit.

Read more: Nicola Sturgeon promises to "save Scotland from Brexit" after talks with UK Government go badly

He said that Labour accepts and respects the outcome of last year’s EU referendum and “we will not block Article 50”.

Asked if that meant he would impose a three-line whip, effectively ordering MPs to vote in favour, he added: “It means that Labour MPs will be asked to vote in that direction next week, or whenever the vote comes up.”

Aides later made clear that no final decision had been taken, leaving open the door to a three-line whip or a lesser order.

Edinburgh MP Mr Murray has yet to confirm his position publicly.

He is expected to do so after the Supreme Court rules on the claim that only MPs, and not Prime Minister Theresa May, have the legal authority to trigger Brexit.

But it is understood that he will vote against starting the UK's divorce from the EU.

His constituency overwhelmingly voted remain last June.

Mr Murray served as Mr Corbyn's shadow Scottish Secretary until he resigned last year in protest at his leader's performance during the EU campaign,

The highly-awaited court judgement will be announced on Tuesday.

The UK Government argues that it has the power to kick-start exit talks and does not need to consult MPs.

Read more: Nicola Sturgeon promises to "save Scotland from Brexit" after talks with UK Government go badly

But ministers are preparing for the possibility they will lose the court case and could table legislation to start the formal exit process as early as the middle of next week.

Justices could also rule that politicians in Holyrood, Stormont and Cardiff Bay have to vote before Article 50 can be triggered.

Several members of Mr Corbyn’s shadow cabinet are also considering rebelling amid concern about the party's strategy on Brexit.

They are understood to be agonising over whether to not to "wave through" Article 50.

Today Mr Corbyn will attack the SNP saying that the party is not standing up for Scotland but sticking up for the establishment as it passes on Conservative austerity cuts.

He will be joined at an event in Glasgow by Scottish Labour leader Kezia Dugdale, just days after he publicly disagreed with her call for a new 'Act of Union'.

Today he will praise Ms Dugdale and Scottish Labour for “leading the fight” against cuts.

An SNP spokesman said: "Jeremy Corbyn’s comments are exactly the sort of carping from the sidelines that Kezia Dugdale warned about when she said that Labour would be unelectable under his leadership.

“Labour in Scotland are stuck in a sorry place between completely irrelevant and totally desperate, and today’s reunion is set to be a prickly affair.

Read more: Nicola Sturgeon promises to "save Scotland from Brexit" after talks with UK Government go badly

“Just last week Jeremy Corbyn fatally undermined Kezia Dugdale’s plans on the constitution - and the attempts to paper over the cracks with this contrived photo op will fool no one."

Meanwhile, Mr Corbyn's senior aide Seumas Milne will stay in his post as director of strategy and communications after quitting as a journalist at The Guardian.

Mr Milne took a year's unpaid leave from the newspaper in 2015 in order to join Labour.

There was widespread speculation that he might return last October, but Guardian News and Media have now announced that he is leaving the newspaper's staff - though the company left the door open for him to write for it again in the future.

A spokesman said: "Following a period of unpaid leave from Guardian News & Media, Seumas Milne has decided to continue in his role as the Labour Party's strategy and communications director, and is leaving the staff of the Guardian.

"We would like to thank Seumas for his brilliant Guardian journalism, and we hope he will write for us again in the future."