Video report by ITV News Correspondent Emily Morgan
Sadiq Khan has led fresh calls for Amber Rudd to resign, as the Home Secretary prepares to fight for her political life over the Windrush scandal.
The London mayor told ITV's Peston on Sunday that Ms Rudd should go due to questions over both her "competence" and her "conduct" around government policy towards migrants.
It came as more than 200 MPs wrote to Theresa May calling for assurances made to the Windrush generation to be written into law in a move that will further increase pressure over the scandal.
Mr Khan said that Ms Rudd had not only failed to show she was in control of her department but also was left facing serious moral questions.
“This a question not just of competence, it’s also a question of conduct," he said.
"I think there needs to be an acceptance that what’s happened to the Windrush generation isn’t an anomaly, it's not due to an administrative error, it’s a consequence of the hostile environment created by this Government.”
He cited vans urging illegal migrants to "Go home" during Mrs May's period as Home Secretary as an example of the Government's troubling attitude towards minorities and migrants.
“Go home – the connotations clearly are racist," he said.
He spoke out as Cabinet figures moved to shore up Ms Rudd over a scandal which threatens to force her resignation - and engulf the wider party.
Transport minister Jo Johnson told Peston on Sunday that Ms Rudd covered a huge policy area, adding: "It's unrealistic to expect a Secretary of State to have seen every single memo that covers all of the policy areas."
He praised her as an "outstanding figure in our politics" and "a very competent secretary of state" in an appearance on Peston on Sunday.
"I'm a big big fan of hers and I think she's got a massive amount to contribute in the very highest levels of Government in the years ahead," he said.
Conservative Chairman Brandon Lewis, who served under Ms Rudd as Minister of State for Immigration from June 2017 to January 2018, said on Sunday he had been aware of targets for removing illegal immigrants.
He said a key memo known to have been copied to Ms Rudd had only discussed an “ambition” and not a firm target as he rejected suggestions she misled a Commons Select Committee over her knowledge of the scheme.
“When Amber Rudd says she didn’t see something, I know she didn’t see it," he told BBC's The Andrew Marr show.
That explanation was rejected by Shadow Home Secretary Diane Abbott, who said he was "hiding behind semantics".
"Beneath the spin, he let the truth slip and sealed her fate. Amber Rudd knew of the targets she pretended didn't exist," she said. "It's time for Rudd to go."
The Home Secretary has apologised after saying she "wasn't aware" of official targets for removing illegal immigrants within her department.
She is due to make a statement in the Commons on Monday to respond to "legitimate questions that have arisen on targets and illegal migration" highlighted by a scandal over the treatment of so-called "Windrush" immigrants from the Caribbean.
The Home Secretary was also given some relief from Vince Cable, the leader of the Liberal Democrats, who said he was not convinced that she had to go.
"I think we should wait and see what she has to say tomorrow," he told the Andrew Marr show.
However, he added: "Clearly she is in considerable difficulty on two scores. Either she’s misled parliament or she was the last person in the country to know that the Home Office was operating a quota system for deportees.”
Some of the so-called Windrush generation have been threatened with deportation, refused access to public services such as healthcare or lost their jobs as a result of “hostile environment” immigration policies.
The Government has offered free citizenship to people from all Commonwealth countries who arrived in the UK before 1973, including individuals who have no current documentation.
Children of the Windrush generation are also included, as well as Commonwealth migrants who already have leave to remain and want to advance their status.
Ms Rudd said some individuals may be eligible for compensation.