Theresa May is facing calls to rethink the “discriminatory” new earnings threshold of £35,000 for non-EU migrants that could starve Britain of vital talent in the teaching, charity and entrepreneur sectors when the changes take effect in April.

Overseas workers who have lived in the UK for five years will have to prove they will be paid the new minimum threshold in order to stay in the country.

Those who fail to demonstrate earnings of more than £35,000 will be denied settlement in the UK and will face deportation according to the new Home Office policy.

The Government temporarily exempted nurses from the new rules last autumn in response to fears about widespread shortages of workers across the NHS.

But the earnings threshold could be applied to migrant nurses in the future should the Government decide to take them off the Shortage Occupation List.

Former Cabinet minister Alistair Carmichael, who was David Cameron's Scottish Secretary before the election, told The Independent that discriminating on the basis of income would harm the UK’s place at the “forefront of the global economy”, while shadow immigration minister Keir Starmer said there were “real concerns” over how key industries would be affected.

Mr Starmer, who served as the Director of Public Prosecutions from 2008-2013, urged ministers to “look more closely” at the threshold, which is currently £20,800 – around £5,000 less than the average UK salary.

A petition launched earlier this week to try to force the Government to rethink the sharp rise in the minimum income requirements has attracted more than 2,000 signatures.

Joshua Harbord, who set up the petition on the Parliament website, told The Independent that he decided to take action because he knew a number of “incredibly upset and scared” people who were set to be affected by the changes but had no one speaking up on their behalf.

“These aren’t the benefits-scrounging, baby-sprouting terrorists that everyone seems so afraid of,” he said.

"They're people who have worked in the UK for years, making friends and families, building homes and communities and contributing to this country's culture and economy.”

The petition, which calls for the Government to scrap the new £35,000 threshold for non-EU citizens, could be debated by MPs if it reaches 100,000 signatures but only needs 10,000 to receive a response from the Government.

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“At the very least, I want an answer from the Home Office, and for the population in general to realise it's impossible to rationalise this insanity,” Mr Harbord said.

"I want them to take responsibility for this incredible mistake, even if they never intend to correct it or make amends.

“Ultimately, I just want my friends and the thousands of other people who face deportation to be allowed to remain in their homes and their jobs."

Mr Carmichael, the Liberal Democrat home affairs spokesman, is writing to Ms May calling on her to publish the Government’s latest assessment on how many people will face deportation when the new rules take effect in April.

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The Home Office’s own assessment of the policy in 2012 admitted that the higher threshold would have a significant impact on teachers, nurses, marketing managers and IT professionals.

Mr Carmichael told The Independent: “Britain must remain open for business – we should be looking to attract the best and brightest not turn them away.

"Discrimination based on income fails to take talent and new sectors like tech start-ups, whose staff might be paid less than £35,000, are essential to keeping the UK at the forefront of the global economy.”