London (CNN)Britain's internal battle over Brexit has reached a new low.

Ahead of a crucial round of talks between London and Brussels over the future trading relationship between the UK and the European Union, the British government made a startling admission: That it would be prepared to break the terms of an international treaty.

The threat was relatively technical -- over an aspect of the withdrawal agreement that allowed the UK to leave the EU at the end of January -- but the admission by a government minister in the House of Commons sent shockwaves through diplomatic circles and raised questions about whether the UK can be trusted on the world stage.

The tumult came with the revelation that the UK is preparing legislation that, in the words of Northern Ireland Secretary Brandon Lewis, will "break international law in a very specific and limited way" by overwriting elements of the Brexit agreement Johnson signed last year.

In public, the government has played down the suggestions that its Internal Market Bill, published on Wednesday, is designed specifically to blow up a part of the Brexit deal called the Northern Ireland Protocol. Quite the opposite -- the government claims it is committed to meeting its international obligations and that the offending passages in the bill merely seek to protect the unity of the UK's four nations in the event that a trade deal isn't reached in the next few weeks.