Tens of thousands of migrants could come to the UK to work for up to a year under the Government’s proposed post-Brexit immigration system.

The new measure, which would be in place until at least 2025, is designed to act as a “safety valve” for the economy and protect sectors reliant on lower skilled overseas labour.

It would be open to nationals from specified countries, regardless of their skill level or whether they have a definite job offer.

Applicants would need to apply for a visa which would be limited to 12 months, at which point a “cooling-off” period will take effect, meaning they could not return under the same route for the next year.

While in the UK, they would not be entitled to access public funds or switch to other routes, bring dependant family members or seek permanent settlement.

The proposed short-term work route forms part of the most significant shake-up of the immigration regime for more than 40 years, set out in a long-awaited White Paper that will apply following the post-Brexit implementation period, which ends in December 2020.

Home Secretary Sajid Javid said: “Today’s proposals are the biggest change to our immigration system in a generation.

“These measures will boost our economy and benefit the British people.”

Adam Marshall, director general of the British Chambers of Commerce, said: “While these proposals are not quite as bad as we had originally feared, it’s no secret that companies across the UK are sceptical about whether the Government’s approach will actually deliver on their practical, real-world concerns.”

Lord Green of Deddington, chairman of Migration Watch UK, said: “These are shocking proposals which run completely against the current of public opinion and which are likely to result in even more massive levels of immigration.”

Shadow home secretary Diane Abbott hit out at the delay in producing the paper, adding: “It will not meet the needs of migrants for certainty, it will not meet the needs of employers for a stable, skilled workforce.”

Noting that the independent Migration Advisory Committee concluded there should be no dedicated route for unskilled labour, the Government’s document said there is no intention to open one.

However, it said employers have become reliant on lower skilled workers from the EU for certain jobs, adding that sectors like construction and social care would find it difficult to adapt immediately after free movement ends.

The paper said: “We have listened to the concerns of businesses … and so there will be a route allowing temporary short-term workers to come for a year.”

The scheme would be open to all skill levels, with no sponsorship requirement.

It would be subject to “tightly defined” conditions and only open to migrants from “specified low-risk countries”.

Numbers admitted through the route may also be restricted, while the Government stressed it was a “transitory” measure and would be subject to a full review by 2025.

The paper said it was “uncertain” how many temporary migrants may come under the system, noting that estimates for the year ending June 2016 suggest around 157,000 EU nationals and 15,000 non-EU nationals arrived for work-related reasons for between one and 12 months.

There would also be a new visa route for skilled workers, who will be entitled to stay for longer, bring dependants and in some cases settle permanently.

This would be open to migrants from all countries, provided they are sponsored by an employer.

As expected, the numerical cap on skilled workers – currently 20,700 a year – would be axed.

While the Government intends to impose a minimum salary threshold, the paper stopped short of committing to a specific figure following widespread opposition to proposals that it should be £30,000.

Former home secretary Amber Rudd, who now holds the Work and Pensions brief in the Cabinet, told ITV’s Peston: “I think it will need to come down in order to address the real need that businesses have for lower-salaried people, who are often skilled people but come in at lower salaries.”

The new skilled work route would be opened up to workers with “intermediate” level skills. Among the occupations that would become eligible are driving instructors, plumbers and restaurant managers.

In an effort to speed up the recruitment process, employers of skilled migrants would no longer be required to carry out a “resident labour market test”.

In other features of the system:

– Anyone who wants to come to the UK would need some form of permission

– EU visitors will not require a visa in advance of travel but an Electronic Travel Authorisation scheme would be introduced

– There would continue to be no limit on the number of international students who could come to study in the UK

– Existing rules on bringing family members to the country, including minimum income requirements, would be extended to settled EU citizens

Introducing the document, Prime Minister Theresa May wrote: “This will be a system where it is workers’ skills that matter, not which country they come from.

“It will be a single system that welcomes talent, hard work and the skills we need as a country.”