Brexit: Buxade says he is worried about Gibraltar (Image: GETTY)
The Cabinet Office Minister Lord Frost said the UK was extending a series of "grace periods" designed to ease trade between Northern Ireland - which remains in the EU single market for goods - and Great Britain while permanent arrangements are worked out.
It provoked a furious response in Brussels, with the EU accusing Britain of going back on its treaty obligations in the Brexit Withdrawal Agreement intended to ensure there is no return of a hard border between Northern Ireland and the Republic.
In an interview with the Financial Times, Mr Sefcovic - who is responsible for overseeing the implementation of the agreement - said the European Commission was now working on "infringement proceedings" against the UK.