Under the draft law, anyone who is deported after making the dangerous journey from France would be banned from re-entering the UK and ever claiming British citizenship.
Home Secretary Suella Braverman would be given a new legal duty to deport illegal migrants, trumping their other rights in UK and European human rights law.
"No more sticking plasters or shying away from the difficult decisions," the interior minister wrote in the Telegraph newspaper, before introducing the legislation in parliament later Tuesday.
"Myself and the prime minister have been working tirelessly to ensure we have a bill that works - we've pushed the boundaries of international law to solve this crisis," Braverman added.
Prime Minister Rishi Sunak said the plan would "take back control of our borders once and for all" - reprising a popular pledge from campaigners like him who backed Britain's Brexit divorce from the European Union.
"This new law will send a clear signal that if you come to this country illegally, you will be swiftly removed," he wrote in The Sun newspaper, ahead of a summit Friday with French President Emmanuel Macron.
The United Nations said Britain's plans would amount to an asylum ban, and urged "more humane" solutions instead.
"The legislation, if passed, would amount to an asylum ban -- extinguishing the right to seek refugee protection in the United Kingdom for those who arrive irregularly, no matter how genuine and compelling their claim may be," UNHCR, the UN refugee agency, said in a statement.
Rights groups and opposition parties say the plan is unworkable and unfairly scapegoats vulnerable refugees.
Christina Marriott, executive director of strategy for the British Red Cross, said the UK would be in breach of its duties under international asylum conventions.
"We wonder if you are fleeing persecution or war, if you are running from Afghanistan or Syria and are in fear of your life, how are you going to be able to claim asylum in the UK?" she told Sky News.
"If they don't have a valid asylum claim, then we are in support of people being returned to countries," she said.
"But what we need for that is a really fair and fast asylum system. And that's what we don't have at the minute."
More than 45,000 migrants arrived on the shores of southeast England on small boats last year - a 60 percent annual increase on a route that has grown in popularity every year since 2018.
Nearly 3,000 have arrived so far this year, often ending up in expensive hotels at taxpayer expense.
The new plan would transfer illegal migrants to disused military barracks, and cap annual asylum claims to a level set by parliament.
The perilous nature of the crossings has been underlined by several tragedies in recent years, including in November 2021 when at least 27 people died when their dinghy deflated.
The government had hoped the threat of a one-way ticket to Rwanda, where migrants would remain if accepted for asylum, would deter the cross-Channel journeys.
But the plan was blocked at the last minute by the European Court of Human Rights (ECHR), which is separate to the EU.
It was then upheld by Britain's High Court, but remains mired in appeals, and no flights to Rwanda have yet taken place.
Reports Tuesday said the government could withdraw from the ECHR if the Strasbourg-based court again intervenes in its latest legislation, although Sunak's spokesman has denied that is in the works.
But it has yet to be confirmed to which so-called "safe third countries" cross-Channel migrants would be deported, other than Rwanda.
In Dover, the scene of an anti-migrant protest and counter-demonstration at the weekend, locals appeared uniformly skeptical about the draft law.
Matthew Stevens, 43, predicted that its stipulations "won't happen".
"Too many people are profiting for it to stop," he said of the criminal gangs who manage the illegal cross-Channel operations.
This report was sourced from Reuters and Agence France-Presse.