Justin Welby has previously spoken out against the legislation, describing it as “morally unacceptable.”

Sources told The Guardian that the archbishop, the most senior cleric in the Church of England, was preparing to take “extremely unusual if not unprecedented” action to amend the bill, which, in its current form, he says could “break the system of international cooperation that promised to help those fleeing war, famine and conflict.”

It is expected that Welby will table additions and changes to ensure safeguards for trafficking victims and children, among others.

Prime Minister Rishi Sunak has said that he is committed to reducing migrant numbers, and to stopping the flow of small boats ferrying people across the English Channel.

Last year the UK saw a significant net increase in immigration to at least 500,000 people. Next week, official figures are expected to show that it has since risen to between 700,000 and one million. Arrivals on small boats via the Channel are also expected to exceed last year’s 45,000.

In Japan this week for a meeting of the G7, Sunak said immigration was “too high” to sustain, and suggested he wanted to reduce it to the 500,000 figure he “inherited” after becoming PM last year.

That would still put the net rate significantly higher than when the Conservatives won the last general election in 2019 — around 271,000 — during which the party promised to cut immigration numbers. Sunak has since distanced himself from that pledge.

The Illegal Immigration Bill seeks to make it easier for the government to remove people who arrive in the country through unapproved methods, swiftly deport those whose asylum claims are rejected, and ban many from re-entering.

Immigration Minister Robert Jenrick said that Welby was “wrong in his assessment of the bill,” adding that it was vital to improve the ability to tackle criminal people-smugglers.

Despite mass opposition to the measures from rights groups, charities, opposition parties and international institutions, some Tory MPs say their party is still not taking a firm enough stance.

Iain Duncan Smith, a former Tory leader, told The Independent: “We set ourselves a task of reducing migration and if we don’t achieve that then the public will mark that down against us.”

He added that the UK has become “addicted to cheap labour,” saying: “We seem … incapable of taking tough decisions and seeing them through quickly.”

Focus in recent weeks has been placed on changing rules about international students in the UK being allowed to bring family members with them. In 2022, 135,788 visas were granted to dependents of foreign students in the UK, a significant increase from 16,047 in 2019.

Prof. Brian Bell, an economist and chairman of the government’s Migration Advisory Committee, said rules around student visas needed to be changed, adding that the current system offered an easy route to remain in the UK after graduation, as it allowed people to stay in the UK for two years, which facilitated them finding low-skilled, low-paid employment.

“An offer to do anything you want for two years seems unnecessary to us, so personally I’ve never been massively in favor of the graduate route,” he told The Telegraph.

Home Secretary Suella Braverman has sought to amend the rules on student and dependent visas, as well as trying to introduce four other plans to reduce migration including raising salary thresholds for foreign workers. However, she has not received the backing of many government colleagues, and has been actively opposed by Chancellor Jeremy Hunt.

Last week, Braverman clashed with the government, saying the UK needed to employ British fruit-pickers over imported labour, as Sunak prepared to announce 45,000 seasonal agricultural visas and a further 10,000 later this year if required.

David Davis, a former Tory minister, told the home secretary to stop blaming others for failings in the immigration system, adding: “You (the government) have to agree on a systematic policy. There’s no point attacking each other, implicitly or explicitly.”

Sir John Hayes, another Tory MP and close ally of Braverman, told The Independent: “Immigration at the level of anything like 700,000 or 800,000 is entirely (unsustainable) and therefore unacceptable — it would be delusional to think otherwise.”

He added: “It will be an unbearable strain. This is the single greatest problem that the government faces.”

Jacob Rees-Mogg, another former minister, said: “I think voters are completely fed up with immigration not being controlled and politicians proposing to do one thing and doing another.”

His colleague Robert Buckland, however, said that Sunak should stop making promises on reducing numbers, and that “the big targets and promises are meaningless.”

He added: “If there’s an issue with some types of students bringing their dependents the government is right to look at that. And I don’t have an issue with raising the threshold on salary requirements.

“But let’s have a sophisticated debate rather than knee-jerk nonsense about the need for British pickers. We have to get real and consider the need to get the economy growing, the need to have people fill shortages in care homes and agriculture – rather than jumping up and down about an overall number.”

An anonymous Tory MP told The Independent that they were worried about a public backlash to an increase in numbers. “If it’s close to a million (migrants) a year, that’s (the size of) three or four Southamptons — we haven’t been building for that. The public will not be pleased.”

Another added: “The frustration is that the government hasn’t been clear on what it wants and what the immigration strategy is. We have to get a grip.

“Constituents get outraged by immigration. But what really gets them p***ed off is illegal migration. We need to have a clear argument on legal migration to explain there’s so many students and so many workers we need.”

The UK’s top universities, meanwhile, have told the prime minister not to include overseas students in immigration figures. In a letter, the Russell Group of 24 elite institutions called foreign students a source of “vital export income” that subsidizes research.

The Federation of Small Businesses said that the political discourse was a distraction.

“We’re currently faced by a situation in which the debate over immigration is splintering into different areas, including refugee policy. This is deflecting attention away from sensible business immigration solutions which the Home Office urgently needs to address,” said Policy and Advocacy Chairwoman Tina McKenzie.

“An easy-to-access and affordable business visa system is what matters to small firms and what the government should be pursuing to tackle the persisting issue of skills and labor shortages.”