THERESA May is facing calls to reveal what she intends to include in a Brexit white paper she has promised to publish.

The Prime Minister will next month produce the key policy document, setting out Britain’s future relationship with the EU.

However, Scotland's Brexit Minister, Mike Russell, said UK Ministers must state what will be in it.

In a letter to UK Brexit minister David Davis, Russell also said the government must explain how the Scottish, Welsh and Northern Irish devolved administrations would be consulted.

"I am writing to you further to your stated intention to publish a white paper in June containing detailed proposals for the future relationship between the EU and the UK," he said.

"My understanding is that this white paper will set out UK positions on the objectives for the future relationship across the range of topics identified and published jointly with the European Commission on the 4 May 2018.

"At the last Joint Ministerial Committee on EU Negotiations on 2 May, the UK Government tabled a proposal for discussions to take place between both officials and ministers on the detail of UK negotiation positions.

"It was intended, and has been described, as being ‘upstream’.

"My understanding of that is that the discussions to take place should do so in advance of the UK Government reaching decisions as to those positions.

"I would therefore like confirmation of your intended path towards delivering this white paper, the scope it will have, and how the Scottish Government – as well as the Welsh Government and Northern Ireland Civil Service – will be involved in its preparation."

The white paper will be published ahead of the crunch European Council on June 28/29.

The EU Commission is keen for Britain to spell out its plan for future customs arrangements at the EU summit.

In response, a UK Government spokeswoman said: "We will engage with the DAs (devolved administrations) on the content of the white paper ahead of its publication."