Members of Parliament (MPs) grilled the government's top legal officer, Attorney General Geoffrey Cox, over legal advice he has given to ministers on the Brexit agreement Prime Minister Theresa May has agreed with the EU.
At the heart of the wrangle is the refusal of the government to publish the full legal advice which details the risk that the border issue between Northern Ireland and Ireland could permanently tie Britain to an arrangement with Brussels.
In a dramatic speech Cox confirmed that Britain will not be able to cancel a so-called backstop clause on the Irish border question without approval from Brussels, reports Xinhua news agency.
It emerged last night that opposition party politicians have called on Parliament to consider contempt proceedings against May's government over its refusal to publish all of the advice given by Cox.
Under the deal backed by the European Council, Britain will leave the bloc next March, with an implementation period starting the next day and continuing until the end of December 2020.
During that period nothing will change and the aim is to agree on a new permanent trade deal with Britain as a non-member of the EU.
The UK, EU and the Irish government have each said they don't want to see the return of a border, but if no deal is reached by the end of 2020, a backstop could be introduced that would keep Britain locked into a customs arrangement with the EU, with no unilateral power to withdraw from it.
It was the latest twist in what is destined to be a roller coaster nine-day in British politics with nobody certain of the outcome.
MPs return on Tuesday for the start of what will be a five-day debate on May's Brexit deal, with a crucial vote taking place on December 11.
May is already on target for a humiliating defeat in a week's time, with politicians from all parties, including her own Conservatives, threatening to vote against it.
The big question in Westminster on Monday night was whether the statement delivered by Cox to MPs will make things better or worse for May, who has insisted the deal she has brokered with Brussels is the best for Britain.
In his statement, Cox admitted that May's deal was a calculated risk, but he believed that if the House of Commons votes down May's proposals next week there will be what he described as great and chaotic disorder.
Cox said he would have preferred to have seen a unilateral right of termination in the Northern Ireland backstop arrangement, but added he supported May's deal because he did not believe Britain would be willingly trapped in it permanently.
"It represents a sensible compromise, it has unattractive elements but these must be weighed up against the realities of the alternatives," he told MPs.
The main opposition shadow attorney general, Labor's Nick Thomas-Symonds responded: "Isn't the reality that the government does not want MPs to see the full legal advice for fear of the political consequences."
A contempt debate will be a political sideshow to the decision in the main debate starting Tuesday on the Brexit deal.
Geraint Johnes, Professor of Economics of Lancaster University, told Xinhua on Monday that it is very likely that the Brexit deal will be vetoed by the parliament on December 11, adding: "It is hard to predict what would follow."
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