THE Scottish and Welsh Governments have warned they will not be able to establish "effective working relations" with the UK's new prime minister unless changes are made to the way devolution works.

Scottish Constitutional Relations Secretary Mike Russell and Welsh Brexit Minister Jeremy Miles both said there must be a change in the "current dynamic" with regards to the relationships between the UK Government and the devolved administrations.

The pair have written to the de-facto Deputy Prime Minister David Lidington, urging a meeting take place "as soon as practicable" with the heads of Government to agree a programme of reform.

They said making these changes must be a "top priority for the incoming prime minister and Cabinet".

In a letter to the Cabinet Office minister, they said: "It will be not be possible to establish effective working relations without firm commitments to change the current dynamic."

It comes just after the UK Government announced a new set of draft principles on intergovernmental arrangements had been agreed with ministers in Edinburgh and Cardiff This included a commitment to "maintaining positive and constructive relations, based on mutual respect" as well as "building and maintaining trust, based on effective communication".

Lidington said: "The draft principles for intergovernmental relations were developed jointly by a working group of representatives of all four administrations.

"The principles are intended to establish a solid foundation for the ways in which all four administrations will work together in the future."

Russell and Miles complained that the review of intergovernmental relations, set up by the UK Government 15 months ago, had made "little progress".

They added: "This, in our view, is almost entirely due to the lack of a commitment to reform on the part of the UK Government."

The Scottish and Welsh politicians said after three years of "mismanaged Brexit negotiations" there was an "urgent need for fundamental reform of the relationship between our Governments".

This must take place whether the UK leaves the EU or not, they added.

"Even before the referendum there was a widespread consensus that the intergovernmental structures are weak and ineffective," Russell and Miles said.

"The experience of repeated failures to involve the devolved governments properly in the negotiations further demonstrates how urgent that task of reform has become."

Meanwhile, Russell said the draft principles agreed with the UK Government "bear little meaning without any firm commitments for further reform".

He demanded: "Whether or not the UK leaves the EU, there is an urgent need for fundamental reform of the relationship between our governments.

"A Heads of Government meeting should be convened as soon as possible to agree a programme for change and a clear timetable."