Trade plans would accelerate break up of UK, claims Welsh minister
Plans for trade between the UK's four nations could "accelerate the break-up" of the union, a Welsh minister said.
UK government plans for the internal market will require Wales, Scotland and Northern Ireland to recognise standards drawn up elsewhere.
Jeremy Miles said the proposals would hamper ministers from setting their own standards for goods.
But Welsh Secretary Simon Hart said the plans would allow Welsh citizens "to thrive within a political union".
The UK government's plans outline which powers currently held by the EU it wants to take on, and which will be given to devolved administrations - such as air quality and animal welfare.
However, the Welsh Government claims it is "misleading" to say the internal market plans would give the devolved governments new powers.
It warns that its own plans for a plastics ban, which go further than the UK government's in England, would be made unenforceable under the new regime.
The English ban, planned for October, covers three types of plastic - straws, stirrers and cotton buds - while Wales wants to ban nine including polystyrene food and drinks containers.
The UK government has said there is "no threat" to devolved governments' powers.
Making the case for the rules in the Spectator, Conservative Welsh Secretary Mr Hart said the proposals would allow "people, products, ideas and investment to move seamlessly between our nations after Brexit".
"This means that if a brewery sells beer in both Swansea and Newcastle, they will not need to create different packaging because they are selling between Wales and England."
High standards, he argued, would be maintained through UK-wide frameworks agreed by all parts of the UK.
"The UK internal market will allow Welsh citizens to thrive within a political union that is so central to economic and cultural life that it seems almost invisible."
The article argued that the union had been "taken for granted" in the past. "It is this arguably complacent approach that is so clearly in the sights of the prime minister," Mr Hart wrote, adding devolution had "too often" been mistaken for the flow of money from bureaucracies in London to Cardiff.
Jeremy Miles, Welsh Government minister for European Transition, made his criticisms of the internal market plans in a letter to the Business Secretary in the UK cabinet, Alok Sharma.
Mr Miles said the "long-term survival of the United Kingdom is under great strain", and the approach "will exacerbate those tensions in a way which, if not addressed, will accelerate the break-up of the union".
The proposals would, he claimed, "prevent the Senedd or Welsh ministers from imposing mandatory requirements relating to lawful sale of goods and services in Wales - even where there were justified by public health objectives, environmental concerns or any other public policy reason".
"This would represent a direct attack on the current model of devolution."
Plans 'ensure businesses can prosper'
Giving examples, the Welsh Government said it would "most likely be impossible" for them to insist on labelling for hormones in beef cattle should the UK government decide to loosen regulations.
The UK government said: "Our proposals ensure businesses can continue to prosper after the transition period ends by guaranteeing their ability to trade freely with each nation of the UK as they have done for centuries.
"Under our plans the devolved administrations will have power over more issues than they have ever had before, and will continue to have the power to regulate within their nations.
"The UK is a world leader in agricultural, environmental and food standards and that will not change. At the end of the transition period, all of these existing standards will be retained in our domestic law and we will not sign any trade deal that compromises our high standards."