EDINBURGH (Reuters) – The heads of devolved governments in Scotland and Wales agreed on Tuesday to work together to try to set a common strategy to thwart the threat of an “unashamed” grab of parliamentary power by London after Britain leaves the European Union.

Wales and Scotland plan to reject legislation which severs Britain’s legal ties with the European Union, once known as the Great Repeal Bill, when it is brought before the devolved chambers in Cardiff and Edinburgh.

That rebuff would not represent a veto in the Brexit process.

It would, however, worsen Britain’s constitutional tensions by forcing the UK government to ignore the expressed wish of the devolved bodies. These decide on most domestic policies such as health and education.

“The UK government’s EU (Withdrawal) Bill is an unashamed move to centralise decision-making power in Westminster, cutting directly across current devolved powers and responsibilities,” Welsh and Scottish First Ministers Carwyn Jones and Nicola Sturgeon said in a joint statement.

“We believe that the bill must not be allowed to progress in its current form.”

Last year’s Brexit vote has heightened strains among the United Kingdom’s four constituent nations because England and Wales voted to leave while Scotland and Northern Ireland voted to remain.

The ministers said the UK government’s approach to leaving the EU so far flouted the principle of devolution, including by preparing a series of position papers concerning Wales and Scotland without consulting the devolved administrations.

The Scottish and Welsh governments argue that returning powers now exercised by the EU to the UK government will imply restrictions on the power of Scottish and Welsh chambers.

“It will now be for the UK government to respond positively to our amendments and move negotiations forward,” the ministers’ statement said.

But Britain’s Scotland minister, David Mundell, has said that the repeal will be a “transitional” arrangement, and it will ultimately result in a boost in devolved parliamentary power.

In July, a report from a committee of lawmakers in Britain’s upper house said Brexit was a fundamental challenge to the future of the UK, and called on the government to set aside party politics and adjust its Brexit approach.