DAVID Mundell today clearly signals that while some extra powers will be devolved to Holyrood post Brexit, others will be reserved to Westminster to help maintain the integrity of the UK’s internal market.

The Scottish Secretary, in a keynote speech during a trade mission to Paraguay, will also call on Nicola Sturgeon, the First Minister, to “decouple” for good Brexit from her campaign for Scottish independence.

Mr Mundell’s remarks come as Jackson Carlaw, revealed that the Scottish Conservatives could take the surprise step of supporting SNP amendments to the UK Government's EU Withdrawal Bill.

The First Minister has denounced the legislation as a “power-grab” by Whitehall and has made clear she will not recommend Holyrood gives its consent as things stand, paving the way for a constitutional crisis with Westminster.

Mr Carlaw told the BBC’s Sunday Politics Scotland: "We don't believe it's the design nor the desire to have this so-called power-grab they visualise but then we want to work to see if there are amendments they are proposing, which we can support.

"And whether or not together we can actually find a way to ensure that the Legislative Consent Motion is something the Scottish Government feel able to support."

Last week, the SNP accused Damian Green, the Prime Minister’s deputy, of “letting the cat out of the bag” after he raised the prospect of “subsidy wars” in the agriculture sector if some form of UK-wide framework on farming payments were not maintained following EU withdrawal.

In his speech, Mr Mundell talks up the importance of further devolution but also of maintaining the integrity of the country’s single market and suggests the key question will be where to set the balance.

He will ask: “Where do we need to retain a UK-wide approach? And where can power returning from Brussels be transferred direct to the Scottish Parliament and other devolved institutions?”

The Secretary of State will go on: “We want to find common sense answers to these questions. For us, that will mean maintaining common, UK-wide frameworks in some areas to protect one of our biggest assets: our UK internal market.”

But he will stress: “Equally, we are clear that we will devolve powers unless there is a reason not to.

“The result will be a Scottish Parliament more powerful than it is today; indeed more powerful than it has ever been.”

Mr Mundell will also touch on intergovernmental relations, saying “private progress has been overshadowed by public rhetoric”.

He will note that despite the “decisive result” in the 2014 independence referendum, the SNP has sought to use Brexit to re-open the issue that divided Scotland so badly.

“Their attempt was roundly rejected in the recent General Election so we now need the issues to be de-coupled for good. Nicola Sturgeon could put that to bed once and for all by ruling out a second independence referendum at her conference this autumn; I hope she does.”

But a spokesman for Keith Brown, Cabinet Secretary for the Economy, dismissed the speech as “rambling” and said it exposed the UK Government’s “confused and chaotic” approach to Brexit, the single market and future trade deals, highlighting the damage that Brexit risked doing to Scotland’s export potential.

He added: “Mr Mundell’s obsession with independence and failure to understand the impact of the EU Withdrawal Bill is at odds with the growing consensus across Scotland that we must protect the powers of the Scottish Parliament from this legislation and that any UK-wide frameworks must be mutually agreed not imposed by Westminster.

“We wish David Mundell every success on this trip but the best thing that could come out of it would be for the Tories to wake up to the economic damage they are causing with their disastrous approach to Brexit.”

Meanwhile today, Mrs May flies to Canada to lay the foundations for a post-Brexit trade deal with the Government in Ottawa.

When Britain leaves the EU, it will fall out of the Comprehensive Economic and Trade Agreement, which was championed by the UK and took seven years to negotiate with Canada.

The PM hopes to use Ceta as a model for a new bilateral arrangement between Britain and Canada to be introduced "swiftly" after Brexit.

Ahead of her visit, Mrs May said: "We are both countries with ambitions to lead on the world stage and progressive values that underpin those ambitions, values including the importance of free trade, and respect for international law.

"When we come together and work as one to project our shared values on the world stage, we form a powerful Union."

The PM leaves for Canada amid calls by Tory colleagues to sack Boris Johnson as Foreign Secretary after he penned a 4,000-word article on Brexit just days before she is due to give a keynote speech on the subject in Florence.

Amber Rudd, the Home Secretary, accused her Cabinet colleague of “back-seat driving” on Brexit and insisted the person in the front seat leading the country’s journey to EU withdrawal was not Mr Johnson but Mrs May.

In a separate development, Ian Blackford, the SNP leader at Westminster, called for the UK Parliament to be recalled if it became clear Mrs May was about to signal a major change in her Brexit policy in her speech in Italy.

“With senior government ministers openly backing opposing and incompatible Brexit positions, while the negotiations are ongoing, Theresa May must urgently clarify who speaks for the UK Government and whether the UK's negotiating position has changed,” insisted the Highland MP.

“The Prime Minister must make a statement to Parliament, recalling MPs if necessary; it would be unacceptable if changes to the UK’s negotiating position were to be announced in Florence, with no parliamentary scrutiny, as media briefings suggest,” he added.