"Unilateral actions are not acceptable," Sefcovic said in a statement.

Sefcovic added that should the UK decide to move ahead with the bill, the EU would need to respond with all measures at its disposal. He also said the potential of the flexibilities proposed by the EU commission had yet to be fully explored, adding: "They can deliver a real difference on the ground."

(Reporting by Charlotte Van Campenhout, Editing by William Maclean)