LONDON (AP) — The man who was Britain’s top legal officer when it signed a divorce deal with the European Union says he won’t support the government’s plan to renege on that agreement less than a year later.

Former Attorney General Geoffrey Cox says he remains a strong supporter of Brexit, but he believes the government will do permanent damage to Britain’s reputation if the country violates its treaty obligations and breaks international law.

Prime Minister Boris Johnson argues that the legislation, to be debated Monday by the House of Commons, is needed to protect the U.K.’s internal market because the EU has threatened to block food shipments from England, Scotland and Wales to the province of Northern Ireland.

But Cox says rather than reneging on its international commitments the government should use the legal remedies contained in the agreement to challenge any unreasonable behavior by the EU.

“I simply cannot approve or endorse a situation in which we go back on our word, given solemnly,” Cox said Monday on Times Radio. “The breaking of the law ultimately leads to very long-term and permanent damage to this country’s reputation.”