Immigration enforcement teams had been set Home Office targets to remove people regarded as having no right to stay in the UK, it has emerged.
Challenged by MPs investigating the problems faced by the Windrush generation, Home Secretary Amber Rudd denied targets are currently used.
An inspection report from December 2015 shows they did exist at that time.
The Home Office said it has never been policy to take decisions arbitrarily to meet a target.
The Windrush row erupted after it emerged relatives of migrants from Commonwealth Caribbean countries who settled in the UK from the late 1940s to the 1970s had been declared illegal immigrants if they could not provide a range of documentation which proved they had lived in the UK continuously.
Some of the Windrush generation have been threatened with deportation, lost their jobs or been refused access to medical treatment.
Their plight has provoked a storm of criticism for the government, with Prime Minister Theresa May apologising for their treatment.
Labour has urged Ms Rudd, who succeeded Mrs May as home secretary in July 2016, to quit over the saga.
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Addressing the Home Affairs select Committee, Ms Rudd said she had asked for more removals of illegal immigrants to take place, but was not familiar with a suggestion from a union official that regional targets were in place.
She said: “We don’t have targets for removals”, adding “if you are asking me if there are numbers of people we expect to be removed that’s not how we operate”.
The home secretary said she would “certainly take a look” at the evidence MPs had heard about targets.
Glyn Williams, a senior civil servant responsible for immigration policy, also said he did not think such targets existed.
The exchange prompted committee chairwoman Yvette Cooper to say the issue needed to be “cleared up” quickly if Ms Rudd and Mr Williams were to avoid claims they were exercising a “lack of grip” on the area.
Lucy Moreton, the general secretary of the Immigration Service Union had told the MPs a national target, broken down regionally, had been set to remove people in the UK illegally, and staff were under “increasing pressure”.
She said the government’s net migration target had been “translated down through the operational arm of the Home Office to a… net removals target that enforcement teams have to meet, so they are aiming to remove a certain number of individuals in any given month”.
The December 2015 inspection report on removals from the Chief Inspector of Borders and Immigration makes clear there had been certain targets at that time.
It says for 2015-16 the Home Office set a target of 12,000 “voluntary” departures of people with no right to remain, split between 19 enforcement teams across the UK.
There was also a target to remove families in the country illegally, though the inspection report said it was not a “useful performance measure”.
In her evidence to the committee, Ms Rudd rejected suggestions that the Conservatives’ goal of reducing net migration below 100,000 had contributed to the Windrush problem.
“The problem here is that people were not properly documented,” she said.
The government has set up a task force to help those affected by the Windrush cases formalise their status.
So far 3,800 calls have been made to the helpline, of which 1,364 were potentially Windrush cases, MPs were told on Wednesday.
Ms Rudd told the Commons Home Affairs Committee that she had known about the problem for months and said officials were still checking how many people had been detained over their supposed immigration status.
“I look back with hindsight and I’m surprised I did not see the shape of it sooner,” she said. “I bitterly, deeply regret that I didn’t see it as more than individual cases that had gone wrong that needed addressing. I didn’t see it as a systemic issue until very recently.”