Theresa May is warned today that she faces a “full-blown constitutional crisis” unless she persuades the other nations of the UK to back her terms for Brexit.

As the Prime Minister prepares to host the leaders of the devolved administrations for talks, a new study has concluded that imposing an exit settlement on them would be “a reckless strategy”.

So far, Ms May has insisted the Brexit negotiations are for her Government to undertake alone – rejecting the Scottish government’s demand to be treated as an “equal partner”.

Today’s report, by the Institute for Government (IfG) think-tank, says imposing a settlement may be “legally possible, given that the UK Parliament remains sovereign”.

But it warns: “This would run contrary to convention and to the spirit of devolution, which recognises the right of the three devolved nations to determine their own form of government.

“It would seriously undermine relationships between the four governments, and increase the chances of Scottish independence and rifts in Northern Ireland’s fragile power-sharing arrangements.”

Nicola Sturgeon, the Scottish First Minister, has already set herself on a collision course with Westminster by publishing a bill to hold a second independence referendum, it notes.

Brexit negotiators are 'in cloud cuckoo land', says man who negotiated Britain's EU rebate

As a result, the IfG describes recent developments as “not reassuring”, adding: “Scottish people may indeed have to choose between their membership of the UK and the EU. But this is not inevitable.”

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The four governments in the UK must agree the “core planks” of the negotiating position before the Prime Minister triggers Article 50, formally starting the Brexit process early next year, it says.

And it concludes: “There is little common ground between these leaders on the future of the UK or almost anything else.

“But the stakes are high. If it proves impossible to find consensus and the dog topples over after a few tentative steps, the result may be a serious breakdown in relations between the four governments (and nations) of the UK.”

The report was timed to coincide with Ms May meeting Ms Sturgeon, Welsh leader Carwyn Jones and Northern Ireland’s leader Arlene Foster, as well her deputy Martin McGuinness, at No 10 today.

Ahead of the first meeting of the Joint Ministerial Council (JMC) since 2014, she insisted she was “ready to listen to proposals” put forward by the first ministers about the Brexit process.

The Prime Minister said: “The country is facing a negotiation of tremendous importance and it is imperative that the devolved administrations play their part in making it work.

“The new forum I am offering will be the chance for them all to put forward their proposals on how to seize the opportunities presented by Brexit and deliver the democratic decision expressed by the people of the UK.”

If the devolved governments agree, a new sub-committee of the JMC, chaired by Brexit Secretary David Davis, will meet at least twice before Christmas.

But the scale of the challenge ahead to achieve agreement was laid bare by a joint call for the three devolved legislatures to be given their own votes on the Brexit negotiating position.

“Such an approach would properly reflect the stated position of the UK Government that the UK is a family of nations, a partnership of equals,” Mr Jones said in a letter to the Prime Minister.