Priti Patel has been branded “clueless” after claiming that labour shortages caused by her tough new immigration plans could be filled by 8.5 million “economically inactive” people in the UK.

The home secretary was speaking as sectors from care homes to construction to farming warned that they will face difficulty recruiting enough staff after the points-based system comes into force at the end of the year.

But official figures from the Office for National Statistics show that the 8.5 million 16- to 64-year-olds currently not seeking work include around 2.3 million students and 2.1 million long-term sick, as well as more than 1.1 million who are retired and 1.9 million who are looking after their family or home. Fewer than 1.9 million of the total were recorded as wanting a job.

The IPPR think tank calculated that Ms Patel’s immigration plans – which replace free movement with a requirement for most migrants to have a job offer worth £25,600 or more – would rule out around 70 per cent of EU workers currently in the country, delivering a “shock” to key sectors of the economy.

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Those excluded would include 90 per cent of EU nationals in the transport and storage sector, 85 per cent in hotels and restaurants, 66 per cent in health and social care and 59 per cent in construction, the think tank said.

Boris Johnson said the changes would mean the UK “welcoming the best and brightest from around the world whilst maintaining full control of our borders”. And Brexit Party leader Nigel Farage hailed them as “a very big step in the right direction”.

But Unison assistant general secretary Christina McAnea said they spelt “absolute disaster” for the care sector, which has not been granted an exemption from the minimum pay threshold.

And the Federation of Master Builders said closing the door on “low-skill” workers would stand in the way of Mr Johnson achieving his promises of massive infrastructure investment and 1 million new homes. Brian Berry, the trade association’s chief executive, said: “It’s simply unrealistic to assume the domestic workforce will fill this gap in the next nine months.”

Dame Sara Thornton, the anti-slavery commissioner, warned that the protection of vulnerable people needs to be “front and centre” of the debate on the changes, as people-traffickers “will seek every opportunity to abuse new immigration policies” during a period of significant upheaval in the system.

Meanwhile, Ms Patel conceded that her own parents – who set up a chain of newsagents after arriving in the UK in the 1960s – would not have been allowed into the UK under her new rules, though she suggested that they might instead have qualified under arrangements for refugees, having faced persecution in Uganda.

Challenged over fears her plans will leave gaps in the workforce, the home secretary told Sky News: “It is about time businesses started to invest in people in this country.

“We have over 8 million people – that is 20 per cent of the workforce – aged between 16 and 64 that are economically inactive right now.

“It is down to businesses to work well with the government and join us in investing in people, levelling up across the UK so we can have wage growth across the entire country.”

Frances O’Grady, the general secretary of the TUC, said it was “not credible” for ministers to expect millions of pensioners, students and carers to enter the workforce.

“Precarious youth and seasonal visas aren’t the answer either,” she said. “The government’s plans will make it easier for bad bosses to exploit migrant workers and drive down pay and conditions for everyone.”

Frances O’Grady has warned of reduced pay and poorer conditions (PA)

Jonathan Ashworth, the shadow health secretary, said: “Priti Patel is clearly clueless about the labour market. Not only has she unveiled an immigration policy that potentially devastates our social care sector – detrimentally impacting on some of the most vulnerable in society – she’s also justifying it by saying that those who are carers, sick or retired should take up these jobs.

“Yet again, the Tories are putting dogma ahead of the needs of the economy and it’s the vulnerable paying the price.”

Liberal Democrat home affairs spokesperson Christine Jardine said that Ms Patel’s comment was evidence that the Conservative government “does not care a jot about people’s lives”.

“Rather than allowing people to travel to the UK and contribute to our economy by working, Priti Patel would rather drag people out of education, out of retirement and out of hospital beds and set them to work,” said Ms Jardine.

Social care providers were loudest in their warnings about the blow the new immigration rules would deal to their sector.

Migrants make up around 17 per cent of staff in adult social care – 40 per cent in London – and there are currently more than 120,000 unfilled vacancies across the country.

The Nuffield Trust health think tank warned Ms Patel’s proposals risked pushing the sector “over the edge”, while Nadra Ahmed from the National Care Association said the government were “either not listening or closing their eyes to the fact that social care needs to be on the shortage occupation list”.

Farmers welcomed changes to increase the number of seasonal workers they can recruit from outside the EU from 2,500 to 10,000 for the coming harvest.

But the National Farmers’ Union urged the government to commit to a full scheme for 2021, so growers can recruit the 70,000 seasonal workers needed on fruit, vegetable and flower farms.

NFU president Minette Batters said that failure to provide an entry route not only for fruit-pickers, but also packers, meat processors and vets, would “severely impact” on their ability to deliver high-quality, affordable food for the public.

And Martin Emmett of the Horticultural Trades Association said that a “significant increase” in numbers of seasonal agricultural worker places would be needed if the industry was to help Mr Johnson deliver his manifesto pledge to plant 75,000 acres of trees a year as part of the UK’s fight against climate change.

“The ornamental horticulture sector, along with other sectors, relies on a seasonal workforce for its essential operations,” he said.