NICOLA Sturgeon and her Welsh counterpart have said they will not support the new Brexit repeal bill, setting up a constitutional crisis on two fronts for the UK government.

Within minutes of the European Union (Withdrawal) Bill being published, the First Minister and Labour’s Carwyn Jones issued a joint statement denouncing it as a “naked power grab” that had “failed utterly” to get the devolved aspect of Brexit right.

The Scottish Greens and Scottish LibDems also labelled the legislation a power grab.

As the Bill will change Holyrood’s powers, the UK government must ask MSPs to approve it through a legislative consent motion (LCM).

Speaking ahead of publication, Scottish Secretary David Mundell said he fully expected a “process row” from the SNP, but did not expect Holyrood would reject an LCM as it would be rejecting more powers.

“This is not a power grab, it’s a power bonanza,” he said, indicating many of the powers currently exercised by the EU would pass over time to the devolved administrations.

However Ms Sturgeon made it clear the SNP would not vote for an LCM, as the Bill did not forward powers as promised, but instead hoarded them at Westminster, and imposed new restrictions on what Edinburgh and Cardiff could do.

Given their hostility to Brexit, the Scottish Greens and LibDems might also reject an LCM.

If a majority of MSPs rejected an LCM it would not amount to a veto over the bill, and the Westminster government could ignore the rejection and impose legislation on Holyrood.

Under the Sewel Convention governing such issues, Westminster remains sovereign.

However Westminster has never imposed legislation on Holyrood since the start of devolution in 1999, and to do so over Brexit would trigger a constitutional crisis.

Ms Sturgeon’s joint statement with Mr Jones said: “This week began with the Prime Minister calling for a constructive and collaborative approach from those outside Whitehall to help get Brexit right.

“Publication of The European Union (Withdrawal) Bill is the first test as to whether the UK Government is serious about such an approach. It is a test it has failed utterly.

“We have repeatedly tried to engage with the UK Government on these matters, and have put forward constructive proposals about how we can deliver an outcome which will protect the interests of all the nations in the UK, safeguard our economies and respect devolution.

“Regrettably, the Bill does not do this. Instead, it is a naked power-grab, an attack on the founding principles of devolution and could destabilise our economies.

“Our two governments - and the UK government - agree we need a functioning set of laws across the UK after withdrawal from the EU. We also recognise that common frameworks to replace EU laws across the UK may be needed in some areas.

“But the way to achieve these aims is through negotiation and agreement, not imposition. It must be done in a way which respects the hard-won devolution settlements.

“The European Union (Withdrawal) Bill does not return powers from the EU to the devolved administrations, as promised. It returns them solely to the UK Government and Parliament, and imposes new restrictions on the Scottish Parliament and National Assembly for Wales.

“On that basis, the Scottish and Welsh Governments cannot recommend that legislative consent is given to the Bill as it currently stands.

“The Bill lifts from the UK Government and Parliament the requirement to comply with EU law, but does the opposite for the devolved legislatures: it imposes a new set of strict restrictions. These new restrictions make no sense in the context of the UK leaving the EU.

“We have explained these points to the UK Government and have set out what we consider to be a constructive way forward in the spirit of co-operation, based on the involvement of, and respect for, devolved institutions.

“Unfortunately, the conversation has been entirely one-sided. We remain open to these discussions, and look forward to coming to an agreed solution between the governments of these islands.”

Scottish Government sources said the key objections were to the Bill restricting the powers of the Scottish Parliament after exit day to amend “retained EU law” after Brexit, and to a restriction of the powers of Scottish Ministers after Brexit.

Scottish Green MSP Ross Greer said the Bill was “a massive power grab that will allow ministers to change huge swathes of legislation without proper scrutiny or consent”.

He said: “The Bill also represents a significant threat to the devolved parliaments in Wales and Scotland, attempting to impose UK-wide arrangements on what are devolved powers rather than negotiate for agreed frameworks.

"Given the volume of changes expected to be made, the Greens want to see provisions on an emergency brake included, to allow parliamentarians to put a halt to these ‘Henry VIII powers’ if ministers are abusing them.

“Green MSPs will push for these changes when consent of the Scottish Parliament is sought. Given what we’ve seen today, we cannot consent to what the Tories propose.”

Scottish LibDem MP and former Scottish Secretary Alistair Carmichael said the bill had “all the hallmarks of another Theresa May disaster”.

He said: “This Government’s executive power grab and support for the most extreme interpretation of Brexit throws in our faces any pretence of being her being constructive and collaborative.

“Liberal Democrats will work with opposition parties to find common ground in support of vital protections, enshrined in European law, from workers’ rights to the environment, as well as ensuring that the principles of devolution are respected.

“These are values that we will defend to the hilt. Theresa May better be ready for a fight.”