NICOLA Sturgeon has vowed to stand alone against the UK government’s final offer on Brexit and devolved powers, making a constitutional crisis all but inevitable.

The First Minister dismissed London's last word on the EU Withdrawal Bill as not being in the national interest, and said no self-respecting MSP could support it.

The Labour government in Wales accepted a compromise on the Bill earlier this week.

However Ms Sturgeon said she regarded the final amendments as unacceptable, as they would still allow the UK government to override the will of Holyrood and impose legislation.

FMQs sketch: Chickens and a plant to deal with as Robison given tepid support

Whitehall sources have made it clear Thersa May does not intend to offer Scotland anything beyond its deal with Cardiff Bay, as that would short-change the Welsh government.

In public, the two sides continue to hold out hope of a deal before the final deadline of May 18, and intergovernmental talks have been pencilled in for week.

But Ms Sturgeon’s emphatic rejection of the UK government’s offer suggests there is now very limited room for manoeuvre.

If MSPs withhold consent for the EU Bill, it will mean the UK government will continue its challenge to Holyrood’s alternative Brexit Bill at the Supreme Court, and Westminster is likely to impose its Brexit legislation on Scotland against Holyrood’s will.

Although such a move has always been a theoretical possibility, it has never happened before, and would take devolution into unchartered territory.

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The dispute is over the distribution of devolved policy areas after Brexit, when powers repatriated from Brussels will be split between Westminster and Holyrood.

The UK wants to retain control over 24 devolved areas, most related to agriculture, fisheries and the environment, for up to seven years after Brexit in order to create UK-wide frameworks to protect the internal market.

Ms Sturgeon says these must be created by consent, not imposed.

At First Minister’s Questions, Scottish Tory leader Ruth Davidson accused Ms Sturgeon of “dancing on the head of a pin” to find excuses not to reach agreement and so stoke a sense of grievance and promote independence.

She said: “There is a deal to be done here. The Welsh have backed it, other parties in this chamber back it, and business wants her to back it, so will the First Minister for once do a deal in the national interest and not in her nationalist interest?”

But Ms Sturgeon said that UK proposals could see the UK government “dictate” policy in devolved areas for seven years, potentially affecting genetically modified crops, and food standards, including opening the door to US chlorinated chicken.

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She ridiculed the UK plan of only creating regulations after a “consent decision” at Holyrood, saying the term covered agreement, silence and outright refusal.

She said: “It is heads they win and tails they lose. I do not think that any self-respecting member of this Parliament should give those proposals the time of day, and this Government will not do that. If that means that we are the only party that is prepared to stand up for the rights and powers of this Scottish Parliament, so be it.”

She added: “This deal is not in the national interest. That is why I will not sign up to it.”

Reinforcing her position, the Scottish Government last night published a legislative consent memorandum stating its reasons for rejecting the EU Bill as it stands.

It said unless key sections were deleted or Holyrood’s consent made essential to UK frameworks, SNP ministers could not recommend that MSPs endorse the EU Bill.

LibDem MSP Tavish Scott said: “We have been constantly assured that SNP Ministers would work to achieve an agreement across the governments of the UK.

“They now look set to depart from that position. Uncertainty for businesses and citizens continues. That is not in Scotland’s interests."

Earlier, Lord Hope of Craighead, formerly Scotland’s most senior judge, said the UK and Scottish governments appeared “very close to agreement”, and praised SNP ministers for pushing back on the original Bill and forcing substantial changes to it.

FMQs sketch: Chickens and a plant to deal with as Robison given tepid support

However he said consent remained the key “sticking point”, with Ms Sturgeon effectively seeking the power to veto frameworks affecting England, Wales and Northern Ireland.

He told BBC Radio Scotland: “One of the boundaries [of devolution] is that the Scottish Parliament cannot legislate in areas that are outside its own territory.

“The UK government is saying ‘we can’t give you a veto over this’, which is effectively what the Scottish government is asking for and it is difficult to get round that final position.”

A UK government source said “If there are things we can do to help the Scottish Government get over the line, then we are listening.”