BRUSSELS (AP) — European Commission President Ursula von der Leyen said Wednesday that the United Kingdom cannot unilaterally change the EU-UK bilateral withdrawal agreement without destroying global trust in the country.

Insisting that chances for a future trade deal are slipping away by the day, von der Leyen told the European Union's legislature that plans by British Prime Minister Boris Johnson to renege on parts of the withdrawal agreement signed by both of them dimmed those hopes even further.

What's more, she insisted that Britain is throwing its good name to the wind by not respecting a deal it signed and approved last December.

"It cannot be unilaterally changed, disregarded,"" she said. "This is a matter of law and trust and good faith," she said in her State of the Union address.

She rubbed it in by quoting from a 1975 speech by British conservative icon Margaret Thatcher.

"Britain does not break treaties. It would be bad for Britain, bad for our relations with the rest of the world and bad for any future treaty on trade," von der Leyen quoted from Thatcher.

Johnson has called his plan to unilaterally rewrite Britain's divorce deal with the EU an insurance policy against the bloc's unreasonable behaviour.

Johnson said a planned law designed to override portions of the Brexit withdrawal agreement he agreed to was needed because the EU might "go to extreme and unreasonable lengths" in its treatment of former member Britain.

Von der Leyen said, however, that the EU will always respect its signature — "We will never backtrack on that."

The European parliament would need to approve any trade deal, and the leader of the biggest group of the legislature, said that any deal coming to parliament would stand no chance if the UK disrespected even the slightest paragraph of the international deal.

"It makes no sense to negotiate a future agreement, (with) a British prime minister who is throwing out of the window the agreement that he signed himself," said Manfred Weber of the European People's Party, the center-right group.

Weber warned: "Great Britain, you are losing your credibility at the global level."