THERESA May has “deepened the constitutional crisis” between Edinburgh and London with her flagship Brexit bill, which runs contrary to devolution, Michael Russell, the Scottish Government minister, has claimed.

His remarks came as David Davis, the Brexit secretary, prepared this morning for the second round of Brussels talks, saying it was time for the UK and EU negotiating teams to "get down to business" with a call for "real progress" to be made on citizens' rights.

The UK Government’s complex EU Withdrawal Bill seeks to repeal the 1972 European Communities Act, which took Britain into the Brussels bloc, and to transpose some 12,000 pieces of EU legislation into UK law.

Nicola Sturgeon has accused the Prime Minister of a “power grab” but David Mundell insisted the legislation would, in fact, produce a “power bonanza” for Scotland.

After the First Minister said she could not recommend Holyrood giving its consent to the bill, the Scottish secretary warned her not to engage in “naked threats and politicking” or she would risk paying a price with Scottish voters for creating a legislative black hole.

However, Mr Russell, who has written to all MSPs urging them to support the Scottish Government’s position, insisted the fault lay squarely at Mrs May’s door.

“This runs absolutely against the spirit of devolution and the practical operation of devolution,” he declared, stressing: “Unless this Bill is altered…we can’t support it; we could not pass a legislative consent motion.”

An LCM is the parliamentary means whereby Holyrood agrees to Westminster legislating on devolved matters.

“I’m willing to negotiate,” declared Mr Russell. “I have spoken to David Davis[and] the first secretary[Damian Green] about this. I will go on having dialogue. We’re keen to see that change.

“But this is not going down well in Brussels, where there is a growing feeling that due process is not being observed by the UK and that’s crucial. The UK has to observe due constitutional process but what it is doing it is ignoring the other legislative bodies and that is not acceptable,” he told the BBC.

The Herald revealed at the weekend how private talks had begun between the UK and Scottish Governments to establish a series of bilateral summits to smooth out any Brexit disagreements; the first is pencilled in for August in Edinburgh against the backdrop of the 70th anniversary of the international arts festival.

Mr Russell freely accepted Holyrood could not block the legislation as an LCM was merely a political convention. But he warned pressing ahead with the bill “would deepen the constitutional crisis that exists…There is a way forward through this. The crisis has been created by the refusal of the UK Government to negotiate sensibly, to put forward proposals that are workable.”

Asked if he was not ramping the crisis up, he replied: “No, I’m not. I’m simply saying we cannot accept this. The Labour Government in Wales are saying exactly the same thing…This is a situation in which the UK Government should have discussed these proposals months ago; it’s time to be sensible.”

But Ian Duncan, the Scotland Office minister, told the BBC’s Sunday Politics programme if the Scottish Government engaged in brinkmanship, it would put people in jeopardy by opposing important legislation.

"The First Minister will have to explain to them exactly what's she's going to do instead of that; it's not good enough simply to posture. You need to be able to say to people who are going to be affected on the day after Brexit that they will be able to go forward and continue to do business as they do now."

Elsewhere, Rebecca Long-Bailey, the shadow business secretary, suggested a Labour government could seek to remain in the European single market and customs union after Brexit.

She said the party wanted to “have our cake and eat it” but acknowledged it was “probably unlikely" they could gain the concessions they wanted in the negotiations.

Tory HQ last night said Ms Long-Bailey’s comments showed Labour’s Brexit policy was a “shambles with members of Corbyn’s inner circle refusing to agree on anything”.