The Home Office has been accused of basing immigration policies on "anecdote, assumption and prejudice" instead of evidence, and having no idea of the effect they have on migrants.
The department shows far too little concern over the damage caused by its failures on "both the illegal and legitimate migrant populations", according to a scathing review from the Public Accounts Committee.
The findings published on Friday, said the Home Office has "no idea" what its £400 million immigration enforcement annual spending achieves, and instead appears to formulate policies not on evidence but on "anecdote, assumption and prejudice".
Committee chairman Meg Hillier said: "The Home Office has frighteningly little grasp of the impact of its activities in managing immigration.
"It shows no inclination to learn from its numerous mistakes across a swathe of immigration activities – even when it fully accepts that it has made serious errors.
"It accepts the wreckage that its ignorance and the culture it has fostered caused in the Windrush scandal – but the evidence we saw shows too little intent to change, and inspires no confidence that the next such scandal isn't right around the corner."
Despite "years of public and political debate and concern", the department still does not know the size of the illegal population in the UK, the report said.
The committee reiterated criticism previously raised by the National Audit Office about the department not estimating the illegal population in the UK since 2005.
The latest report said the Home Office had "no answer" to concerns that "potentially exaggerated figures calculated by others could inflame hostility towards immigrants".
The department does not know whether hostile environment policies have deterred illegal migration, it added.
A lack of evidence and "significant" lack of diversity at senior levels has created "blind spots" in the organisation, the report said, describing the Windrush scandal as demonstrating the "damage such a culture creates".
The department does not know why so many migrants were released from detention because they could not deport them as planned last year (62% compared with 58% in 2018), the report said.
It also warned the Home Office was "unprepared for the challenges the UK's exit from the EU presents to its immigration enforcement operations", adding that the department had been unable to provide evidence, when asked in July, that it had begun discussions with EU counterparts on international operations, including regarding "the return of foreign national offenders and illegal migrants".
The committee said it was not convinced the department is "sufficiently prepared" to properly safeguard the existing, legal immigrant population in the UK, while also implementing a new immigration system and responding to the Covid-19 pandemic.
The committee gave the Home Office six months to come up with a detailed plan to make sure its decision-making is led by data and evidence so it can analyse its work, particularly with regard to tackling illegal migration.
Minnie Rahman, campaigns and public affairs manager for the Joint Council for the Welfare of Immigrants, said the report paints a "very accurate picture of a clueless, careless and cold-hearted Home Office.
"It is but the latest in a slew of reports to slam the Home Office's working culture and practices."
The charity echoed the committee's calls for change, adding: "Immigration policy and practice must be based on robust evidence, proper staff training and a new culture of respect and care for individuals."
A Home Office source said: "The Home Secretary agrees with the assessment made by the Public Accounts Committee of historical issues at the Home Office.
"She has spoken at great length how the department puts process before people and is why she has committed to implementing the findings of the Wendy Williams review into Windrush."