The author of a report into the Windrush scandal is warning there is a “grave risk” of similar failures happening again if the government does not implement its recommendations.
Wendy Williams told BBC Radio 4’s The Westminster Hour the Home Office still needed to “make good on its commitment to learn the lessons”.
People from the Commonwealth were told wrongly they were illegally in the UK.
The Home Office said the home secretary intends to “right those wrongs”.
Ms Williams’ warning comes as the country prepares to pay tribute to the outstanding and ongoing contribution of the Windrush Generation and their descendants.
National Windrush Day on Monday will commemorate the day 72 years ago when the ship HMT Empire Windrush arrived at Tilbury Docks, Essex, carrying migrants to help fill jobs in the UK.
Many of the projects planned for the day will take place online due to the coronavirus crisis.
An estimated 500,000 people now living in the UK who arrived between 1948 and 1971 from Caribbean countries have been called the Windrush generation.
They were granted indefinite leave to remain in 1971 but thousands were children travelling on their parents’ passports, without their own documents.
Changes to immigration law in 2012 meant those without documents were asked for evidence to continue working, access services or even to remain in the UK.
Ms William’s review, published in March, was critical of the “hostile environment” policy operated by successive governments to tackle illegal immigration.
She told The Westminster Hour the Home Office and ministers “should have realised the impact” of the legislation on different groups of people.
The report concluded the Home Office had shown “ignorance and thoughtlessness” on the issue of race when some people were incorrectly told they did not have the right to be in Britain.
Ms Williams, an inspector of constabulary, previously called on the government in March to provide an “unqualified apology” to those affected and the wider black African-Caribbean community.
Speaking earlier this year, Home Secretary Priti Patel said in House of Commons there was “nothing I can say to undo the pain” but added “on behalf of this and successive governments I am truly sorry for the actions that span decades”.
Ms Williams said the risks posed by the controversial policy were flagged to the Home Office by “other groups and stakeholders” but because ministers ignored the warnings the outcome of the Windrush scandal was “both foreseeable and avoidable”.
Her report made 30 recommendations.
She said: “The Home Office has a very stark choice. It can decide not to implement my recommendations and, if that happens, then I think there is a very grave risk of something similar happening again.”
The Home Office said in a statement the home secretary has been clear that the mistreatment of the Windrush generation by successive governments was “completely unacceptable and she will right those wrongs”.
As part of that effort Ms Patel has launched the Windrush Cross-Government Working Group, it announced.
Co-chaired by Ms Patel and Bishop Derek Webley, the group is intended to bring together stakeholders and community leaders with government officials to address the challenges faced by the Windrush generation and their descendants.
Ms Williams also said the compensation scheme for victims of the scandal is not demonstrating the benefits it should and applications need to be processed quickly and sensitively, with interim payments made where possible.
However, the Home Office pointed out that the scheme made the first payment within four months of opening and has offered claimants over £640,000 in the first year.
It said that Ms Patel will give an update on her intended response to the review before the summer recess and will then provide a detailed formal response in September.
It added the Commonwealth Citizens Taskforce has granted over 12,000 people a form of documentation that confirms their right to remain in the UK and guarantee their access to public services.