Keir Starmer’s plan to force employers to be less reliant on overseas staff and instead train UK-based workers may not lower net migration, researchers have found.

Skill shortages are just one of the factors contributing to employers’ demand for migrant workers, according to the University of Oxford’s Migration Observatory.

Local workers can be difficult to attract because of poor pay and conditions, a report published on Wednesday found, while hundreds of thousands of recent arrivals who have entered the UK on student visas or as dependants will compete with domestic workers for jobs.

The prime minister last year said the government would impose new rules on employers so they train UK-based workers.

“If employers want to bring workers from overseas, then they must also invest in the skills of workers already in Britain,” Starmer said in May.

“At the same time, we will wean our national economy off its reliance on cheap labour from overseas. The end result will be a reformed immigration system that no longer ignores the millions of people who want the opportunity to train and contribute.”

In a 13-page briefing, the Observatory concluded that the government could struggle to impose recruitment changes on particular industries.

“It is difficult to create effective incentives in the immigration system that explicitly encourage employers to invest in domestic training. A sectoral approach could encourage ‘free riders’, while an individual approach is difficult to monitor,” the report said.

“Significant data gaps prevent a comprehensive overview of how migration is affecting the UK’s skills base.”

Increasing the domestically trained workforce did not automatically lead to lower migration, the report said.

“Skill shortages are just one factor that contribute to employers’ demand for migrant workers – for example, local workers can be difficult to attract into certain roles because of poor pay and conditions. Recruitment of migrants is also driven by migrants’ choices to come to the UK, regardless of any shortage,” it said.

Restricting the number of visas issued to overseas workers only affects a small share of the labour supply, the report said.

Of the 3.45 million non-EU citizens who received visas since Brexit and still had a valid immigration status at the end of 2024, only 17% were main applicants on work visas, according to Home Office data.

“Most migrants have work authorisation but are not main applicants on work visas, instead arriving on family or dependant visas, or as students or refugees.

“Work visas post-Brexit drove much of the increase in the migrant workforce in some industries, such as health and care, but had a much smaller impact in others, such as construction,” the briefing said.

Ben Brindle, a researcher at the Observatory and co-author of the report, said: “Any plan to make the UK labour market less reliant on overseas staff and encourage employers to train UK workers instead may not fill skills gaps in the UK economy.

“There isn’t a fixed number of jobs in the economy. For example, they dropped during Covid and then increased again afterwards. The UK could train more engineers, but demand for engineers might increase, too. This higher demand could cancel out the higher supply of engineers, leaving a skills gap

“In addition, migrants on work visas only make up part of migration system. People that come as dependants, students, and on other routes also have work rights. Employers could still hire these migrants.”

The Home Office has said that employers wishing to recruit engineers, IT workers and telecommunication staff from abroad will have to show they are training the domestic workforce too.

From this summer, representatives of employers in key sectors will be expected to have an approved workforce plan in place.

The government ended overseas recruitment of care workers in 2025 and ended visa access for middle-skilled jobs such as butchers and chefs.

A UK government spokesperson said: “Net migration is now at its lowest level in five years, down by more than two-thirds under this government. In the year to September 2025, visas issued to main applicants across all work routes dropped by 27%.

“Alongside major reforms announced by the home secretary to fix our broken immigration system, making sure people who come here contribute fully and give more than they take, we are building a structured, evidence-led approach covering skills, migration and wider labour market policies – including pay and conditions.”