The United Kingdom will have “no choice but to act” if the European Union is not flexible over the Northern Ireland protocol, foreign secretary Liz Truss warned on Thursday.

Truss made the remarks during a phone conversation with European Commission vice-president Maros Sefcovic in which she argued that the lack of agreement over the Northern Ireland protocol was “a matter of internal peace and security” that could threaten the 1998 Good Friday peace deal that ended decades of sectarian violence, a period known as The Troubles.

The NI protocol is a key part of the post-Brexit agreement that imposes border checks on goods entering Northern Ireland from the rest of the UK.