Britain's international reputation is at stake regarding its intentions to override the Brexit Withdrawal Agreement, according to the United Kingdom's former Attorney General Geoffrey Cox.

The Brexit supporter was the government's top legal advisor when the Withdrawal Agreement was drawn up and pushed through Parliament in January.

Cox has now said he will vote against the government's Internal Market Bill when it comes before Parliament this week, saying he can not support efforts to overwrite the agreement with the European Union.

Members of Parliament are debating the legislation amid growing criticism that breaching international law would jeopardize the UK's standing in the world.

His position is believed to influence some Conservative MPs on how they will vote on the bill. The EU has warned the UK it could face legal action if it does not ditch controversial elements of the bill by the end of the month.

In an article for The Times on Monday, Cox accused British Prime Minister Boris Johnson, who asked him to resign in February, of doing "unconscionable" damage to Britain's international reputation.

Cox points out that tariffs and customs procedures on certain goods entering Northern Ireland from Britain were part of the agreement.

But as free trade negotiations continue to flounder some MPs are growing increasingly concerned that food imports may be blocked from Britain to Northern Ireland.

"There can be no doubt that these were the known, unpalatable but inescapable, implications of the agreement," he wrote in The Times.

"We, the British government and Parliament, have given our word. Our honour, our credibility, our self-respect and our future influence in the world all rest upon us keeping that word.

"It is unconscionable that this country, justly famous for its regard for the rule of law around the world, should act in such a way," he said.

Johnson has warned that Brussels could "carve up our country" without the new bill, and has stepped up his rhetoric to drum up support for it.

The UK left the EU on Jan 31 under the terms of a Withdrawal Agreement. When the transition period ends on Dec 31, the UK will leave the EU's single market and customs union. If efforts to secure a free trade deal fail the two sides would revert to basic international trading rules.

Speaking on the BBC's Andrew Marr Show on Sunday, the government's Justice Secretary Robert Buckland said the powers in the proposed bill amounted to a "break the glass in emergency provision if we need it" and said he did not believe they would be used.

Conservative former prime ministers Theresa May and John Major have voiced outrage against the bill, and Major united with fellow former Labour Party prime minister Tony Blair to urge MPs to reject the legislation.

The UK's chief trade negotiator, David Frost, is in Brussels for informal talks with EU officials this week, with the chances of achieving the sought after free trade deal now looking more remote week by week.