Under fierce criticism in the Commons, the prime minister refused to review the harsh rules she introduced or explain why warnings that it would trap people who arrived in Britain legally decades ago were ignored.
Instead, Ms May said the crackdown – which has turned employers, the NHS and landlords into de facto “border guards”, critics say – enjoyed widespread support.
“Up and down this country, people want to ensure that the government is taking action against those people who are here in this country illegally,” she told MPs.
“It isn’t fair that people who work hard day-in-day-out, who contribute to this country, who put into the life of this country, are seeing people who are here illegally accessing services in the same way,”
The prime minister ducked Jeremy Corbyn’s criticism that the “hostile environment” had also hit the Windrush arrivals – who had been detained, denied healthcare and threatened with deportation.
The Labour leader said Amber Rudd, the current Home Secretary had “inherited a failing policy and made it worse”, adding: “Isn’t it time she took responsibility and resigned.”
A clearly angry Mr Corbyn pointed out that a Home Office memo four years ago – when Ms May was home secretary – had warned her policies would “provoke discrimination against Commonwealth immigrants.
He said her own communities secretary, Eric Pickles, had warned the “costs and risk considerably outweigh the benefits”, adding: “Why did she ignore his advice?”
The crisis had been caused by the “environment she created in six years as home secretary when she knew full well of the problems the Windrush generation were facing”, Mr Corbyn alleged.
But the prime minister blamed the 1971 Immigration Act, which had left the children of immigrants without documents, insisting: “That is what we are now putting right.”
She said the government was helping the Windrush generation, who “are British, they are part of us and we are ensuring that they remain here and are able to continue to live their lives here”.
David Lammy, the former Labour minister, said that - in 2011 - he wrote to then immigration minister Damian Green about a Tottenham constituent who came to the UK in 1956 at the age of four.
He said: “In 2011, he was told he could no longer work and he did not have British citizenship. He [Mr Green] wrote to me and basically said 'tough'.”
Mr Lammy asked Ms May to explain what compensation would be provided – and a guarantee that no “vulnerable and scared” people who ring the Windrush hotline would be face action by immigration officials.
The prime minister said the compensation scheme would be set out “shortly”, adding the government had “made clear there is no question of taking enforcement action when people ring that hotline”.
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