The SNP has vowed to reject the Repeal Bill as it stands after a meeting with Conservative ministers ended in stalemate.
Damian Green, the First Secretary of State, was told by Scottish ministers in Edinburgh that the UK Government’s flagship Brexit bill is a “direct threat to the devolution settlement”.
Speaking after the meeting on Wednesday, Scotland’s Brexit secretary Michael Russell, said the proposed legislation is “impractical and unworkable”, adding they will call on Holyrood to vote against it unless there are “serious and significant changes”.
“It is a blatant power grab which would take existing competence over a wide range of devolved policy areas, including aspects of things like agriculture and fishing, away from Holyrood, giving them instead to Westminster and Whitehall,” Mr Russell said.
Legally speaking, Westminster could plough on even if MSPs withhold their consent.
But ignoring the will of Holyrood could trigger an unprecedented constitutional crisis.
The bill is designed to transfer EU law onto UK statute books at the point of Brexit.
The administrations in London and Edinburgh have clashed over what happens to Brussels powers covering devolved areas once they are repatriated to these shores.
UK minsters say Brexit provides a powers “bonanza” for Holyrood, but insist the devolved competences should be held in Westminster while returned laws are sifted through.
Some of the responsibilities, such as agriculture and fisheries, will need to be subject to common frameworks to protect Britain’s single market, the Tories say.
The SNP said this must be done through agreement between Holyrood and Westminster as equals rather than by imposition.
Questioned on the “power grab” claims, Mr Green told the BBC: “I hope as these talks go on we will be able to convince them that there is absolutely the opposite of the intention of a power grab.
“We want more powers to come to the devolved administrations. That has to be done in the context of keeping free trade within the United Kingdom, but we’ve agreed more talks in a few weeks’ time.”