One of Boris Johnson’s most senior law officers has quit in protest at the government’s plans to break international law over Brexit.

The dramatic move by Lord Keen of Elie QC, the Advocate General for Scotland and a justice minister, was finally confirmed by No.10 Downing Street hours after he handed in his resignation.

A last ditch bid by the PM to hold onto the minister failed, despite moves to reassure Tory MPs that a compromise plan could be worked out to avoid the UK breaching the EU’s ‘divorce’ treaty.

In his resignation letter, Keen had a withering verdict on the legality of the government’s policy.

“I have found it increasingly difficult to reconcile what I consider to be my obligations as a Law Officer with your policy intentions,” he said.

A Downing Street spokesperson said: “Lord Keen has resigned as Advocate General for Scotland. The Prime Minister thanks him for his service.”

The Advocate General was last week rumoured to be on the edge of resigning over the cabinet minister Brandon Lewis’s bombshell admission that the government’s new Internal Market Bill “breaks international law in a specific and limited way”.

Keen had sparked ridicule on Tuesday when he told peers that he felt that Lewis had “answered the wrong question” when making his now infamous comment about breaking international law.

But he faced humiliation when Lewis told MPs on Wednesday his colleague had been flat wrong to dispute the government’s stance.

During his own grilling before a parliamentary committee, Johnson had told MPs that “conversations on that matter [Keen’s possible resignation] are still continuing”, adding “I can’t comment on that matter because it’s still, as I understand it, to be resolved.”

But within minutes, the news was confirmed.

Shadow Attorney General Lord Falconer said: “This has been a week of chaos from the government’s own law officers, whose legal advice has been renounced by its own government and the voice of the law officers has been muted, and their authority is completely shot.

“This has been a farce that shames the entire government”.

The government’s most senior legal civil servant, Sir Jonathan Jones, quit last week after clashing with attorney general Suella Braverman on points of law, including the new legislation to break international law.

Keen’s departure seemed likely after government sources told HuffPost UK on Tuesday night that Keen was not speaking for the government when he suggested Lewis had misspoken.

And in evidence to the Northern Ireland select committee, Lewis rammed home his message that his words were official policy in line with legal advice of the Attorney General Suella Braverman.

“I’ve spoken to Lord Keen. When he’s looked at the specific question I was asked last week, he has agreed with me that the answer I gave was correct. That answer I gave reflects the government legal advice,” he said.

Lewis had been replying to a question from Tory grandee Sir Bob Neill, who has since threatened a rebel amendment to the legislation that would give MPs the final say on any breach of the EU-UK Withdrawal Agreement on Brexit.

Lewis told MPs: “I read out something very specific because I wanted to ensure that what I said, to make sure that I was giving the House a straight answer.”

The cabinet minister also insisted that the government intends to deploy its “break the law” provisions in parallel with using EU arbitration mechanisms, rather than exhausting the Brussels route first.

“Even if we end up in a situation where we need to use the ‘safety net’ we do that at same time [as going down the EU route],” he said.

Earlier, Lib Dem MP Alistair Carmichael seized on the chaos as he urged Johnson in prime minister’s questions to publish the full legal advice from all his law officers.

“Last week the Secretary of State for Northern Ireland said that the Internal Market Bill would breach our obligations under international law. Yesterday, the Advocate General for Scotland said the Secretary of State was wrong to say that,” Carmichael said.

“Today, the Secretary of State says that the Advocate General wrong to say he was wrong. It’s of course possible that they are both right in saying that the other is wrong. But surely on an important matters such as this requires clarity.”

Johnson refused the request to publish the full advice.

But Lewis sparked a fresh backlash from the EU when he refused to say whether he would abide by the outcome of the arbitration process agreed with Brussels for any disputes over the Brexit divorce treaty.

Asked directly if the UK would abide by the outcome of such arbitration, Lewis replied: “To get into a hypothetical about what would happen is an unhelpful and dangerous place to be.”

Committee chair Simon Hoare replied that “there are many people in prison” who don’t like “the ruling of the judge” but they accept it nevertheless.

Irish politician Neale Richmond was swift to condemn Lewis’s latest remarks.

Meanwhile, the UK faced fresh anger from the EU after Lewis refused to guarantee that the UK would abide by the outcome of any disputes process agreed with Brussels.

European Commission president Ursula von der Leyen jibed the PM, quoting Margaret Thatcher’s belief that “Britain does not break treaties”, as the Brexit row reignited once more.

In her annual State of the Union address to the European Parliament, Von der Leyen said both sides had agreed the Withdrawal Agreeent was the only way to guarantee the Northern Ireland peace process.

She quoted Mrs Thatcher, as saying: “Britain does not break treaties. It would be bad for Britain, bad for relations with the rest of the world and bad for any future treaty on trade.”

The EU chief added: “This was true then and this is true today. Trust is the foundation of any strong partnership.”