The U.K. said European Union proposals to resolve post-Brexit economic disruption in Northern Ireland “don’t go far enough,” as the two sides remain deadlocked in negotiations which could end in a trade war.

“I’m not sure they would quite deliver the kind of ambitious freeing up of trade between Britain and Northern Ireland that we would like to see,” Brexit minister David Frost told a parliamentary committee on Monday, referring to the EU’s offer to reduce customs checks on goods crossing the Irish Sea. “The gaps between us remain significant.”

Britain and the EU are locked in more talks on their post-Brexit settlement, with Boris Johnson’s government threatening to unilaterally suspend the divorce deal covering Northern Ireland due to its negative impact on trade.

Following the split from the EU, the U.K. agreed to an effective customs border in the Irish Sea in order to avoid creating a hard border on the island of Ireland. It now wants to amend the arrangement, arguing that it harms Northern Ireland’s economy and is not working as intended.

Yet if Britain reneges on its commitments regarding Northern Ireland, the EU could weigh terminating the whole post-Brexit trade deal, according to people familiar with the matter.

On Monday, Frost also reiterated his desire to see the removal of the role of the European Court of Justice in overseeing the Northern Ireland protocol.

He appeared to dispute recent newspaper reports that the U.K. may consider agreeing to a “Swiss-style” governance arrangement for Northern Ireland, where an arbitration panel would be set up to deal with disputes about the protocol but the ECJ would retain a role in interpreting questions of EU law.

“We’re not interested in arrangements which keep the court in by some other name, at one remove, or in some other way,” Frost said. “We can’t have the Court of Justice settling disputes between us in this protocol in future.”