LABOUR has called on Scottish Conservative MPs to back its amendment to key Brexit legislation today to protect Scotland's devolution settlement.

And as MPs debate the Report Stage of the EU Withdrawal Bill, the SNP urged Jeremy Corbyn to “get off the fence” and back its drive to keep the UK in the European single market and customs union. An amendment put forward by the Nationalists is seen as an attempt to flush out Labour rebels, 50 of whom voted for a soft Brexit the last time the issue was voted on at Westminster.

Concerns have been raised not just by the Scottish opposition parties but also from within the Scottish Tories after David Mundell, the Scottish Secretary, having promised to bring changes to the Brexit legislation at Report Stage to allay fears of a so-called “power-grab,” failed to do so. The promised amendments will now be introduced when the House of Lords considers the Bill next month.

But Lesley Laird, the Shadow Scottish Secretary, and Sir Keir Starmer, the Shadow Brexit Secretary, have written to the 13 Scottish Tory MPs urging them to back their party’s own amendment to allay fears of a power-grab before peers consider the legislation.

Whitehall prefers the process of powers from Brussels going first to Westminster and then being passed onto Holyrood, so that common frameworks can be agreed to avoid harming the UK’s internal market.

But opposition parties want the powers to go to Edinburgh first and for common frameworks to be agreed in this context. Scottish Tory MPs, who have privately criticised ministers handling of the process, are also keen for the devolution process not to be circumvented.

“The EU Withdrawal Bill as it stands drives a coach and horses through the devolution settlement. That is simply unacceptable,” declared Ms Laird.

"The Secretary of State has broken his promise that this legislation would be fixed to protect the principles of devolution.”

She stressed how the bill could still be changed before it went to the Lords if Scottish Conservative MPs agreed to Labour's amendment to “protect the devolution settlement".

The amendment says UK-wide frameworks will only be proposed if they are necessary to: enable the functioning of the UK internal market; ensure compliance with international obligations; ensure the UK can negotiate, enter into and implement new trade agreements and international treaties; enable the management of common resources; administer and provide access to justice in cases with a cross-border element and safeguard the security of the UK.

It adds ministers “shall only create UK-wide frameworks if they have consulted with, and secured the agreement of, the effected devolved administrations”.

Yesterday evening in the wake of Scottish Tory concerns, Ruth Davidson emerged from talks with the Prime Minister, claiming “huge progress” had been made in intergovernmental work on the bill.

Talking to reporters in Downing Street, the Scottish Tory leader said: “We are working towards the same ends, there’s not a huge amount between the two parties…

“This is about what the framework of a new UK after we leave the EU looks like; how is power held, what are these shared frameworks, how are they agreed rather than imposed, what is the backstop to them? If there is a dispute in future, what is the dispute resolution mechanism?”

Ms Davidson added: “This is all very technical, complicated stuff. It will take time to work through it. There are many of us who are frustrated that it’s taken as long as it has and continues to take time. But my understanding is that there has been huge progress this week and we should be hopeful.”

Elsewhere, after last week empty-chairing the Labour leader at a soft Brexit summit of opposition parties, the SNP urged Mr Corbyn to join it, the Liberal Democrats, the Greens and Welsh Nationalists in supporting UK membership of the single market.

"Time is running out to prevent the economic catastrophe of an extreme Tory Brexit,” insisted Stephen Gethins, the Nationalists’ Europe spokesman.

"Jeremy Corbyn must now get off the fence, show some leadership and get behind efforts to protect our vital membership of the single market and customs union before it is too late.”

The Fife MP added: "If Labour continue to support reckless Tory plans for a hard Brexit, they will be guilty of destroying jobs and slashing the incomes, livelihoods and living standards of millions of people."

Meanwhile, a BMG Research poll found that 57 per cent said they would back another public vote if the UK left the EU with no deal.