European Commission vice president Maros Sefcovic told German news website Der Spiegel that problems with the Northern Ireland Protocol – a way to maintain a free-flowing land border on the island of Ireland after Brexit – meant the UK “broke international law” in trying to get round the arrangement.
But he said he is still confident that a compromise can be found between the two sides, although he admitted it will not be easy.
Mr Sefcovic told Der Spiegel he is “pragmatic” about Foreign Secretary Liz Truss taking on responsibility for post-Brexit negotiations with the EU, after Brexit minister Lord Frost resigned earlier this month.
But he warned that if Ms Truss was to trigger Article 16, a move that would effectively unilaterally suspend the treaty agreed between the UK and the EU, it would throw into jeopardy “the foundation of the entire deal” reached between the two sides.
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Ms Truss has said she remains prepared to invoke Article 16 if issues are not resolved.
But Mr Sefcovic said: “This is a very distracting element in the discussions. You try to achieve something together and – bam – there’s the threat of Article 16 again.
“It touches on the fundamentals of our relationship.
“The Northern Ireland Protocol was the most complicated part of the Brexit negotiations, and it is the foundation of the entire deal. Without the protocol, the whole system will collapse. We must prevent that at any cost.”
He added: “London has breached a great deal of trust, which we must first rebuild. But I believe we can find a compromise.
“The EU and the United Kingdom are strategic partners – and they should treat each other as such.”
In the lead-up to Christmas, soon after taking on the role of chief Brexit negotiator for the UK following the resignation of Lord Frost, Ms Truss threatened to suspend the Northern Ireland Protocol if the EU does not end the role of the European Court of Justice as the final arbiter on the matter.
She had said she wants talks with the EU over Irish trading arrangements to “pick up the pace” in the new year.
The Foreign Secretary had also insisted earlier this month that the UK’s position on the Northern Ireland Protocol has “not changed” following the departure of Lord Frost as Brexit minister.