The European Union on Monday launched legal action against the UK for unilaterally changing trading arrangements for Northern Ireland that the EU argues breach the Brexit deal agreed with Westminster.

The move by the EU could ultimately lead to financial penalties on the UK or trade tariffs being imposed.

The UK Government said it will respond in due course to the notification of legal action and defended its move to ease post-Brexit border checks to smooth trade with Northern Ireland.

Northern Ireland effectively stayed in the EU’s customs union and single market under the Brexit deal.

This got around the need for border checks on the island of Ireland — but introduced such checks on goods entering Northern Ireland from Great Britain.

The UK last month said it would temporarily waive rules set begin on April 1 that would have required firms sending food between Great Britain and Northern Ireland to provide additional customs paperwork.

The UK claims its actions in extending grace periods for Northern Ireland businesses do not breach its commitments.

“We have received the letters from the European Commission and will respond in due course,” a UK Government spokesman said in a statement.

“We’ve been clear that the measures we have taken are temporary, operational steps intended to minimise disruption in Northern Ireland and protect the everyday lives of the people living there.

“They are lawful and part of a progressive and good faith implementation of the Northern Ireland Protocol.”

The Commission said: “The European Commission has sent today a letter of formal notice to the United Kingdom for breaching the substantive provisions of the Protocol on Ireland and Northern Ireland, as well as the good faith obligation under the Withdrawal Agreement.

“This marks the beginning of a formal infringement process against the United Kingdom.

“It is the second time in the space of six months that the UK government is set to breach international law.”

European Commission vice-president Maroš Šefčovič said: “The Protocol on Ireland and Northern Ireland is the only way to protect the Good Friday (Belfast) Agreement and to preserve peace and stability, while avoiding a hard border on the island of Ireland and maintaining the integrity of the EU single market.

“The EU and the UK agreed the Protocol together.

“We are also bound to implement it together. Unilateral decisions and international law violations by the UK defeat its very purpose and undermine trust between us.

“The UK must properly implement it if we are to achieve our objectives.

“That is why we are launching legal action today.

“I do hope that through the collaborative, pragmatic and constructive spirit that has prevailed in our work so far on implementing the Withdrawal Agreement, we can solve these issues in the Joint Committee without recourse to further legal means.”