Boris Johnson's administration suffered a heavy defeat in the House of Lords as peers vowed to reject the "morally wrong" and "illegal" Brexit legislation that enables minister to break international law.
With 365 votes to 169, members backed a "regret" amendment, condemning the contentious provisions of the legislation which they warned would "undermine the rule of law and damage the reputation of the United Kingdom".
The rejection of the disputed parts of the Bill by members of the House of Lords sets the scene for a showdown between the unelected chamber and Commons.
It could lead to a lengthy parliamentary "ping pong" where legislation is passed between the two Houses.
The Archbishop of Canterbury Justin Welby, former Commons speaker Baroness Boothroyd and Conservative former leader Lord Howard of Lympne were among many in the upper house to criticise the Bill, which has already cleared the Commons despite opposition from some senior Tories.
Speaking in support of the amendment, Liberal Democrat peer Lord Fox said: “We all know this Bill is illegal and we know it flouts important constitutional issues and threatens devolution.
“More than that, we know it has already eroded trust in our institutions and we know it is damaging the reputation of this country, which promotes the rule of law.
“Finally, and perhaps most insidiously, we know that any law that seeks to permit the executive to break laws is morally wrong.”
Referring to the “egregious clauses” in the Bill, Labour frontbencher Lord Stevenson of Balmacara argued the Government’s “pre-emptive action has placed the United Kingdom in the wrong” and damaged Britain’s “international reputation as a defender of the rule of law”.
He added: “When the history of these troubled months comes to be written it will not be kind to the current Prime Minister and his Cabinet.”
Responding, Cabinet Office minister Lord True told peers: “We share a full and fundamental respect for and belief in the rule of law.”
Defending the Government’s “limited, contingent proposals” in the Bill, he added: “It does not accept that these safeguard provisions render our country, as has been claimed, an international pariah or justify, as was asserted, murderous actions by others. People are still talking to us.”
But Lord Judge, a former lord chief justice, who proposed the regret amendment, said: “The fact of the matter is the law would be broken. There can be no getting away from it.
“You don’t have to be a lawyer to understand the rule of law. And you certainly don’t have to be a lawyer to understand when you are giving powers away.
“You don’t have to be a lawyer to understand the reputational damage to the United Kingdom.
“We cannot resile from the fact that we are breaking the law if this Bill is enacted.”
The legislation contains powers which gives ministers the opportunity to override the Brexit divorce deal, something the Government has acknowledged would breach international law.
A compromise reached in the Commons to head off a Tory backbench rebellion, which gives MPs a vote before the powers can be used, has been dismissed by some peers.
Additional reporting by PA Media.