The Home Office is to hold an internal review of its handling of the Windrush scandal, Theresa May has said.
She told MPs it would have "full access" to all relevant documents, including policy papers and case files.
Her announcement came as Labour prepares to try and force ministers to release all government papers relating to Windrush cases since 2010.
Jeremy Corbyn said the crisis had been "made in the Home Office" under Theresa May's leadership.
At Prime Minister's Questions, he asked Mrs May whether she "felt a pang of guilt" about the resignation of Amber Rudd over the issue earlier this week.
The prime minister said the inquiry would seek to "learn lessons" from the treatment of Windrush families, some of whom have been detained and threatened with deportation after their right to remain in the UK was questioned.
It will aim to complete its work before the summer recess in July.
She said "speed is of the essence" and new home secretary Sajid Javid "will be commissioning a full review of lessons learned, independent oversight and external challenge".
The review, she said, will have "full access to all relevant information in the Home Office, including policy papers and casework decisions".
The Conservatives are expected to oppose a Labour motion which would see all relevant internal documents handed to the Commons Home Affairs Committee.
The rarely-used procedure - called a "motion for a return" - involves asking the Queen to direct her ministers to provide the requested documents.
Opening the debate in the Commons, shadow home secretary Diane Abbott asked Conservative MPs if they understood "how voting against this motion will look to the Commonwealth and will look to the Windrush generation here".
She said she doubted Mr Javid's claim to be abandoning the "hostile environment" tag attached to the government's immigration policies, saying his predecessor Amber Rudd had been a "human shield" for its architect, Theresa May.
She added: "Unless and until the prime minister announces the abandonment of the form of hostile environment which she instituted and demonstrates that that be the case then we should all understand that the policy remains in place."
Mr Javid said the Labour motion would divert resources "into a massive, open-ended fishing expedition".
He told MPs he would be regularly writing to the Home Affairs Select Committee with progress including a monthly report with the latest information on detentions and deportations.
"This review will seek to draw out how members of the Windrush generation came to be entangled in measures designed for illegal immigrants, why that was not spotted sooner, and whether the right corrective measures are now in place," he said.
Mr Javid also said "members of the hard left" had greeted his appointment with racist abuse, challenging Mr Corbyn to "denounce them".
Ms Abbott said that "everyone on this side of the House without exception condemns the names he has been called".