The Prime Minister's promise of a parliamentary vote on the proposed Brexit deal should be written into legislation, the lawyer who led the successful legal battle against the Government has insisted.
Speaking during the House of Lords Brexit bill debate, Lord Pannick, who represented the lead claimant, Gina Miller, in the Article 50 case, argued a political commitment was no substitute for an obligation in law, pointing out that circumstances, including Prime Ministers, could change.
Lord Pannick also stressed it should be for Parliament to decide if there was to be a deal or not.
During his speech Lord Pannick praised Ms Miller, who along with other campaigners won the historic legal action in the Supreme Court "in the face of quite outrageous racist and sexist abuse", which led to a declaration that Parliament must authorise the triggering of Brexit.
Lord Pannick also stressed the Lords' need to "scrutinise a Bill of enormous importance to the future of this country", adding the bill required "amendment".
Former cabinet secretary Lord Butler of Brockwell said he backs an amendment calling for the public to be consulted again on the Government's final Brexit deal.
Lord Butler's comments came as the Lords debated the European Union (Notification of Withdrawal) Bill for the second day.
Lord Butler said that while he accepts Britain is leaving the single market to regain control of immigration, a final deal should be put to the people.
Lord Butler said: "Is the outcome of last June's referendum to be interpreted as meaning that a majority of the United Kingdom want to leave the EU whatever the terms? The Government clearly thinks so.
"But on a matter of this importance has not the Government a duty to be sure before our departure becomes final?
"My lords, one has to ask why those who base their arguments for Brexit on the will of the people are now opposed to consulting the people on the outcome of the negotiations.
"One has to suspect that they fear that they will get a different answer. If so, we ought to know."
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Britain will continue to help tackle Europe's migrant crisis after Brexit, the prime minister Theresa May has confirmed.
Speaking at a summit of EU leaders in Malta the PM referred to the issue of migration from Libya across the Mediterranean as one of the "biggest challenges that Europe is facing" and pledged that the UK would continue its support to tackle the issue after leaving the EU.
She said: "We've agreed what we need is a comprehensive but a coordinated approach.
"The UK has already contributed significantly to the effort but we will continue to do so and we will continue to do so even after we leave the European Union because we want to continue to be a good friend and ally to the European Union as we build a global Britain standing tall in the world."
Mrs May also said that looking ahead to upcoming Brexit negotiations what she wanted was to build a "strong partnership" with the EU as "we're not leaving Europe, we're leaving the EU".
European Union leaders have announced that they will be embracing a plan to "stem illegal flows into the EU" as part of "a sustainable migration policy" to ensure effective control of Europe's external border.
Speaking at a summit in Malta on Friday European Council President Donald Tusk said the 28 countries in the Union had agreed to "work with the IOM to step up voluntary returns from Libya to countries of origin" as well boosting training, equipment and support to the Libyan coast guard.
The agreement was reached less than 24 hours after Italy and Libya reached a deal which called for more support for the Libyan Coast Guard and the "humanitarian repatriation" of migrants, with a possible economic deal in the pipeline.
European leaders are watching the relationship between Theresa May and Donald Trump with suspicion, according to ITV News Europe Editor James Mates.
At the first EU summit since President Trump was sworn in, French President Francois Hollande said Donald Trump was putting "unacceptable pressure" on the union.
European Commission president Jean-Claude Juncker echoed Mr Hollande's criticism, suggesting Mr Trump "does not know Europe".
Although leaders believe that she did good work on convincing Trump to continue supporting Nato, she also pressed her counterparts to commit to spending 2% of GDP on defence, as per Nato rules.
There are suggestions that, if the Trump administration continues being antagonistic, EU leaders think the UK will need to choose whether to enjoy a close relationship with Washington, or with Brussels.
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Theresa May used a walking tour of Valletta in Malta to talk with some of the key players that will take part in upcoming Brexit negotiations.
The Prime Minister and her European counterparts visited some of the capital's historic sites during the 30-minute excursion.
Mrs May took turns to speak to German chancellor Angela Merkel, European Commission president Jean-Claude Juncker and European Council president Donald Tusk.
Mrs May chatted to well-wishers along the route from the Grandmaster's Palace to St John's Cathedral.
She admired the interior of the cathedral, before walking with Mr Juncker to the Barrakka Gardens, and then taking in the view across the bay with Mr Tusk.
She ignored shouted questions by reporters along the route.
European Union leaders have signalled caution and confusion about America's potential new direction under Donald Trump.
European Commission president Jean-Claude Juncker said he did not feel threatened by the new president, but "there is room for explanations because of the impression that the new administration does not know the EU in detail but in Europe details matter".
Austria's Christian Kern said: "Today we have pretty mixed feelings, to be honest, because the tangible aspects of Mr Trump's policies are raising some concerns.
"It's not a threat, it could be a catalyst for a strong, more united Europe. It is an alarm call to see if we are the right track."
French President Francois Hollande stressed the need for a united Europe in the face of uncertainty from the US.
Asked what he thought of leaders, like those in Hungary and Poland, who were leaning towards Mr Trump, Mr Hollande said: "Those who want to forge bilateral ties with the US are of course well understood by the public.
"But they must understand that there is no future with Trump if it is not a common position. What matters is solidarity at the EU level. We must not imagine some sort of external protection."
German chancellor Angela Merkel said: "Europe has its destiny in its own hands. I believe that the more strongly we make clear that we will define our own role in the world, the better we will be able to cultivate our transatlantic relationship."
Theresa May has reassured leaders that Brexit will not mean paring back relations with EU countries.
The prime minister was holding talks with leaders like Germany's Angela Merkel, Spain's Mariano Rajoy, and Austria's Christian Kern at a one-day European summit in Malta.
Following their conversation, in which she updated Mr Rajoy and Mr Kern on the UK's preparations for Brexit, Mr Rajoy said her speech "clarified many things".
A Downing Street source said: "They agreed that it was important to think about the future relationship as well as the detailed exit arrangement, so that we can give greater certainty for people and businesses who want to live and work in each other's countries."
They also agreed that an early deal on the rights of EU citizens in the UK, and British citizens in the EU, was desirable.