(CNN)Embattled British Prime Minister Theresa May lost a key ally late Sunday with the resignation of Home Secretary Amber Rudd, who quit after claiming she "inadvertently misled" government over targets for the deportation of illegal immigrants.
UK Home Secretary Amber Rudd resigns over immigration scandal
Rudd resigned Sunday amid a growing scandal over the government's mistreatment of the so-called "Windrush generation," men and women from the Caribbean who arrived in Britain in the 1950s and 60s, but in recent years have been declared illegal immigrants despite having lived in the country for decades.
She becomes the fourth high-ranking minister to resign from May's government in the past six months. It puts further pressure on May, already struggling to maintain government unity over faltering Brexit talks.
Rudd had been under pressure to step down over her involvement in the affair, following allegations that members of the Windrush generation -- so named after the ship that had brought hundreds of Caribbean migrants to Britain -- had recently been refused medical care, denied housing and threatened with deportation.
On Monday, Rudd was due to face a fiery session in the House of Commons. Instead, May is expected to announce Rudd's replacement, an influential role that comes at a delicate time for the UK government as its negotiates Britain's exit from the European Union.
Parliament will also debate a petition Monday calling for an amnesty for "anyone who was a minor that arrived In Britain between 1948 to 1971," which would include the Windrush generation.
The Home Affairs Select Committee questioned Rudd last week over government targets for the removal of illegal immigrants. Rudd told the committee she had no knowledge of targets. However, the Guardian on Sunday published a memo written by Rudd in which she said deportation quotas had been set.
"Since appearing before the Select Committee, I have reviewed the advice I was given on this issue and become aware of information provided to my office which makes mention of targets. I should have been aware of this, and I take full responsibility for the fact that I was not," Rudd said in her resignation letter.
The Prime Minister accepted Rudd's resignation, writing: "I was very sorry to receive it, but understand your reasons for doing so."
May said that Rudd had answered questions from the House of Commons and the Home Affairs Select Committee in good faith, but that she understood her decision to step down in the light of Rudd's review of the advice she'd been given.
On Saturday, more than 200 Members of Parliament from across the political spectrum signed a letter addressed to May accusing Rudd of making up immigration policy "on the hoof" in a bid to overcome the scandal.
Labour MP David Lammy, who wrote the letter, said the controversy was an "international embarrassment" for Britain. Speaking on Sky News on Sunday, he said the letter was a "cross-party effort to ensure the Windrush generation get the guarantees they need, they know where they stand and we move on from this situation."
Lammy said Rudd's resignation must not detract from the core issue of seeking justice for Windrush citizens.
"At its heart this crisis is about a system that was allowed to dehumanise and victimise Windrush British citizens... That policy must now be reviewed, and the Home Office must move quickly to compensate and grant citizenship to the Windush generation," he tweeted.
The Windrush generation came to Britain to help in the postwar rebuilding efforts, following the devastating effects of World War II.
May's government recently said the Home Office destroyed landing documents for members of the Windrush generation, meaning some of them and their children faced deportation after decades living in Britain because they don't have the correct paperwork.
May apologized to Caribbean leaders for any "anxiety" caused by the records destruction, which occurred when she was home secretary under the previous administration.
May was Rudd's predecessor, serving as Home Secretary from 2010 to 2016 under then-Prime Minister David Cameron. Policies from that time included sending out vans to tell illegal immigrants to "go home," making regular deportations and resistance to rescue operations that pulled drowning migrants from the Mediterranean.
Blame for the scandal was quickly directed toward May. Tom Watson, the deputy leader of the opposition Labour Party, tweeted: "I see Amber Rudd is carrying the can for the person originally responsible for this scandal -- Theresa May."
The Windrush generation came to symbolize the seismic demographic changes that took place in post-war Britain, when hundreds of thousands of people came to the United Kingdom from former British colonies, known as the Commonwealth.
But in recent years, successive British governments have sought to appear tough on illegal immigration, and their descendants are now struggling to prove a citizenship status they previously took for granted.
Rudd last week apologized for and told the House of Commons the UK would work to ensure citizenship for the Windrush generation.
Rudd's resignation further imperils May's government. After a badly timed election last year, the prime minister does not have a majority in the UK parliament and is struggling with Brexit negotiations. Reaction to Rudd's resignation ranged from regret to renewed predictions that May's position is under threat.
Foreign Minister Boris Johnson said she was a "fine colleague" who cares deeply about the people she serves.
Michael Gove, the Environment Secretary -- who has been suggested as a possible replacement -- said he was "so sad" about the departure of a "brave" and "principled" colleague.
Rudd was appointed as home secretary in July 2016. She previously served in the government as secretary of state for energy and climate change, parliamentary under secretary of state for climate change and assistant government whip.
Rudd has been a member of Parliament since 2010, though she won her constituency in Hastings and Rye by only a few hundred votes in 2017.
May shook up her cabinet last January, but Rudd and other major figures kept their jobs.