British Prime Minister Boris Johnson's government will press ahead on Monday with legislation to scrap rules on post-Brexit trade with Northern Ireland, setting up further clashes with the EU.
The legislation, which would replace parts of the post-Brexit deal that was agreed on in 2020 by Britain and the EU, is due to be sent back to parliament's lower house for a second reading.
Foreign Secretary Liz Truss said London's priority was to protect a 1998 peace deal that Ireland, the US and other countries have said could be put at risk by replacing parts of the Northern Ireland Protocol.
"This legislation will fix the problems the protocol has created, ensuring that goods can flow freely within the UK, while avoiding a hard border and safeguarding the EU single market," Ms Truss said on Sunday.
"A negotiated solution has been and remains our preference, but the EU continues to rule out changing the protocol itself, even though it is patently causing serious problems in Northern Ireland, which therefore means we are obliged to act."
Britain plans to stop some checks on goods moving to Northern Ireland from the rest of the UK and it is challenging the role played by the EU's court.
The EU's ambassador to Britain said on Sunday that the UK's plans were illegal and unrealistic.
"It is a treaty that we signed, ratified and even went through a general election in this country," Joao Vale de Almeida told Sky News.
The European Commission has launched legal proceedings against Britain, which could lead to a trade war.
EU officials say Mr Johnson is trying to regain support among legislators in his Conservative Party after he narrowly won a confidence vote this month.