DAVID Mundell's admission some EU powers will not be devolved to Holyrood after Brexit was today described as a "complete betrayal" of promises made to Scotland by the Leave campaign.

The Scottish Secretary, in a keynote speech during a trade mission to Paraguay, said he wants to see "common UK-wide frameworks in place" and does not want to see any "barriers to free trade within the UK".

Joan McAlpine, the SNP MSP and convener of Holyrood's Europe Committee, said his comments confirmed the Tories’ plans for a Brexit power grab.

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"David Mundell has now explicitly conceded the UK government plans to take control of devolved powers returning from Brussels – the first time since devolution that powers in areas like agriculture and fishing would not reside at Holyrood," she said.

"That fundamentally undermines the founding principles of devolution – and it’s a complete betrayal of the Leave campaign’s promises to Scotland.

"The Scottish Government are not opposed in principle to agreeing UK-wide frameworks where powers are returning from Brussels. But that must be by mutual agreement and not imposed on Scotland against our will."

She added: "This is a far cry from the “powers bonanza” that David Mundell previously boasted about. It also appears to undermine his Holyrood Tory colleagues, who claim to be interested in helping to stop a power grab.

"All devolved powers returning from Brussels must come to Holyrood – anything less would breach the founding principles of devolution which people voted for."

During the EU referendum, the Leave campaign promised that "major" powers over areas such as agriculture "would automatically be devolved to Holyrood, not Westminster".

The claims may have prompted some voters in Scotland to back exiting the European Union.

Research has suggested around a third of SNP voters backed leaving the bloc.

Speaking in the South American country today Mundell said: "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.

"I am not prepared to see barriers emerge to trade within the UK, which would be extremely damaging for Scottish firms and for business across the UK. Equally, we are clear that we will devolve powers unless there is a reason not to."

Despite his comments that some powers from Brussels would be held onto at Westminster, he insisted: "The result will be a Scottish Parliament more powerful than it is today, indeed, more powerful than it has ever been."

His intervention comes a day after it emerged Scottish farmers stood to lose around two billion euros of funding if European Union agriculturall subsidies are replaced by a single UK-wide scheme post Brexit.

The SNP said calculations from Scottish Parliament Information Centre (SPICe) revealed that if Scotland received the same per capita funding as the UK average, the reduction in funding for Scotland would be just under 2.3 million euros.

Agricultural subsidies dominated Scottish debate on Brexit last week after First Secretary of State Damian Green, effectively Theresa May's deputy, suggested a standard scheme, controlled by Westminster, would be needed to prevent different systems from operating in various parts of the UK.

Scotland’s population is about 10 per cent of the UK total, but currently Scottish farmers receive 16 per cent of the UK’s overall common agricultural policy (CAP) funding under the EU system , including 85 per cent of less-favoured area payments which are given to farmers in remote areas and where the land is difficult to cultivate.