This handout picture released by Sky News on Jan 31, 2020 shows a farewell message projected onto the White Cliffs of Dover, on the southern coast of England, the day the UK formally leaves the European Union. (TIM P. WHITBY / SKY NEWS / AFP)

France and Ireland went on the offensive over the UK’s obligations in any post-Brexit trade deal, escalating a war of words that risks overshadowing the start of negotiations with the European Union next week.

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Arriving at a meeting of national governments in Brussels to sign off the EU’s opening goals for the talks, representatives from Paris and Dublin warned Prime Minister Boris Johnson that the bloc won’t back down on some of its most fundamental demands -- including that Britain continue to play by the EU’s rules, something Downing Street has ruled out.

After the EU’s 27 member states formally adopted their mandate on Tuesday, the UK said it will unveil its own on Thursday before negotiations between the two sides start on Monday.

The mandate “is to protect the interest of Europeans,” said French Europe Minister Amelie de Montchalin, who insisted that the EU won’t agree to anything if it doesn’t come with guarantees to ensure fair competition and access to fish in UK waters.

For Ireland, it is just as important that Johnson sticks to the promises he made in Britain’s divorce agreement with the EU to prevent the return of customs checks on the Irish border.

“Without good faith and trust building, a future relationship isn’t going to be easy,” Irish Foreign Minister Simon Coveney said. “And so, if there isn’t progress on the infrastructure needed to implement the Irish protocol as part of the Withdrawal Agreement in the next few months, then I think that is going to be a very worrying signal for whether or not it’s going to be possible to conclude something sensible before the end of the year.”

After the EU’s 27 member states formally adopted their mandate on Tuesday, the UK said it will unveil its own on Thursday before negotiations between the two sides start on Monday. They have until the year-end to reach an agreement or Britain will default to trading with the EU on terms set by the World Trade Organization, meaning the returns of tariffs and quotas.

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For the EU, the mandate is important because it gives chief negotiator Michel Barnier a framework he must work in. While there remains some room for compromise, the EU’s position makes clear that the UK must stick to EU standards in many areas, especially in the area of state aid.

Johnson has said he would rather walk away without a deal than accept being bound by EU rules. For Britain, regaining political independence and freedom from the bloc’s legal system will take priority over securing a trade deal by the deadline of the end of this year, according to the premier’s spokesman.

A special committee of Johnson’s Cabinet agreed to the UK’s negotiating mandate on Tuesday, spokesman James Slack told reporters. “It was a smooth process to agree our approach, which will restore our economic and political independence,” he said.