International protections for refugees are “not inconvenient obstructions to get round by any legislative means necessary”, the Archbishop of Canterbury said as he lambasted the Government’s plans to tackle the small boats crisis.

In a withering attack on the Illegal Migration Bill, the Most Rev Justin Welby argued it risked “great damage” to the UK’s reputation at home and abroad and said it was “morally unacceptable” to leave the poorest countries to deal with the migration crisis.

The top cleric urged a rethink of the flagship legislation aimed at ensuring people who arrive in the UK in small boats would be detained and promptly removed, either to their home country or a third country such as Rwanda.

It includes provisions that would limit the ability of the European Court of Human Rights (ECHR) to prevent the deportation of asylum seekers.

The clampdown has been prompted by Prime Minister Rishi Sunak’s pledge to “stop the boats” bringing migrants across the English Channel.

More than 6,000 migrants have been detected crossing the channel so far in 2023.

To cope with the numbers, the Government plans to use disused military camps and a barge as accommodation centres.

But critics argue the flagship immigration reforms break international law and threaten modern slavery protections.

Criticising the Bill as it faces its first test in the upper chamber, Mr Welby said: “We need a Bill to reform migration.

“We need a Bill to stop the boats.

“We need a Bill to destroy the evil tribe of traffickers.

“The tragedy is that without much change this is not that Bill.

“This Bill fails to take a long term and strategic view of the challenges of migration and undermines international co-operation rather than taking an opportunity for the UK to show leadership.”

Highlighting the existing global agreements on refugees, Mr Welby said: “While now inadequate, what those conventions offer is a baseline from which to build a globally shared understanding of what protection must be given to refugees.

“They are not inconvenient obstructions to get round by any legislative means necessary.”

He added: “Even if this Bill succeeded in temporarily stopping the boats, and I don’t think it will, it won’t stop conflict or climate migration.”

Mr Welby went on: “Of course we cannot take everyone and nor should we, but this Bill has no sense at all of the long-term and the global nature of the challenge that the world faces.

“It ignores the reality that migration must be engaged with at source as well as in the channel.

“As if we as a country were unrelated to the rest of the world.”

Mr Welby added: “It is isolationist, it is morally unacceptable and politically impractical to let the poorest countries deal with the crisis alone and cut our international aid.

“This Bill is an attempt at a short-term fix.

“It risks great damage to the UK’s interests and reputation at home and abroad, let alone the interests of those in need of protection or the nations who together face this challenge.

“Our interests as a nation are closely linked to our reputation for justice and the rule of law and to our measured language, calm decision and careful legislation.

“None of those are seen here.

“This nation should lead internationally, not stand apart.”

We simply cannot continue with a situation whereby year-on-year tens of thousands of people make the dangerous, illegal and unnecessary journey across the channel in circumvention of our immigration controls

While he agreed with the “sentiment” of a Liberal Democrat attempt to block the legislation, he said: “It is our duty to change, not to throw out the Bill.”

Mr Welby added: “I urge the Government to reconsider much of the Bill, which fails to live up to our history, our moral responsibility and our political and international interests.”

Home Office minister Lord Murray of Blidworth faced jeers and shouts of “shame” in the Lords as he argued the Bill was a “compassionate response” to the small boats problem.

He said: “We simply cannot continue with a situation whereby year-on-year tens of thousands of people make the dangerous, illegal and unnecessary journey across the channel in circumvention of our immigration controls.”

He added: “We must stop the boats. This Bill, in conjunction with the other steps the Government is taking, is a necessary, urgent and indeed compassionate response to the daily challenge posed to the integrity of our immigration system. We must act now.”

Liberal Democrat and former senior police officer Lord Paddick argued the legislation was “a low point in the history of this Government”.

He said: “This Bill seeks to systematically deny human rights to a group of people desperately seeking sanctuary.”

Labour frontbencher Lord Coaker said: “In response to a broken system that is failing, we have a Government playing fast and loose with our place in the world and our respect for international law. This must change.”