Downing Street said leaders of the devolved administrations must not “undermine” Brexit negotiations.
Asked about calls for different parts of the UK to be able to opt in or out of the single market, the Prime Minister’s official spokeswoman said a united UK negotiating position is “vital to protect the UK’s interest as a whole”.
“We need to make sure we are not putting up barriers to trade within the UK.”
She added: “We have been very clear that we should be working together to secure the best possible deal for the whole country.
“We expect representatives of the devolved administrations to act in that way and to in no way undermine the UK’s position.”