Thousands of Commonwealth and Caribbean-born people living in England and Wales did not hold any passport at the time of the last census, newly released documents show.
Data drawn from the 2011 household survey provides the first official indication of the size of populations that have come under the spotlight in the wake of the Windrush scandal.
Experts identified a group of more than 20,000 Commonwealth-born residents who arrived in the UK prior to 1971 and had no passport at the the time of the census as being most at risk of being caught up in immigration enforcement measures.
Tables published by the Office for National Statistics on Friday show there were a total of 264,125 residents who, in the census seven years ago, said they were born in the Caribbean.
Of those, 144,395 had arrived in the UK before 1971, while the remaining 119,730 came to the country between 1971 and 2011.
Among the pre-1971 arrivals, 132,421 held a UK passport at the time of the census, while 5,193 reported that they did not hold any passport.
Of the Caribbean-born residents who arrived between 1971 and 2011, there were 66,562 UK passport holders and 2,358 who did not have any passport.
A second data set compiled from the census showed that in total just over three million people born in Commonwealth countries other than the UK were resident in England and Wales.
This included almost 600,000 people who arrived before 1971, with 21,053 of those stating that they did not hold any passport, while 541,616 had UK passports. Others held non-British travel documents.
The ONS said it should be noted that the “no passport held” category counts the number of residents who reported not holding a passport on census day in March 2011.
This does not necessarily mean that they have never held a passport or that their residency status has not been fixed in other ways, the statistical agency added.
Madeleine Sumption, director of the Migration Observatory at the University of Oxford, said: “The new census data are consistent with our previous analysis of Commonwealth migrants living in the UK who arrived before 1971, but provide a more accurate count and also give us more detailed information about the physical documents people hold.
“It shows that 90% of around 600,000 Commonwealth migrants who came to the UK before 1971 and were still resident here in 2011 held a British passport and that 57,000 did not.
“Perhaps more importantly though, it shows that about 21,000 pre-1971 Commonwealth migrants did not have any passport at all.
“This group is likely to be at highest risk of getting into trouble with the immigration enforcement measures that led to the so-called ‘Windrush’ cases.
“Of course, people without a passport may still be able to demonstrate their legal status with other evidence, such as a naturalisation certificate or another immigration document.”
Ministers faced a furious backlash over the treatment of the Windrush generation – named after a ship that brought migrants to Britain in 1948.
People who had arrived before 1973 were automatically granted indefinite leave to remain under the 1971 Immigration Act, but the Home Office did not keep a record of those allowed to stay or any documentation confirming their status.
While many of those who arrived have taken British citizenship or have official documents proving their status, others have struggled to source paperwork demonstrating they are lawfully resident.
Those who have been living legally in the UK for decades have lost their jobs, been denied access to NHS treatment, benefits and pensions, had their driving licences withdrawn and been warned they face deportation.
Under emergency Government measures, thousands of people will be offered the chance to obtain British citizenship free of charge and without the requirement to take language tests.
A compensation scheme for those affected by the failings will also be introduced within weeks.
Earlier this week new Home Secretary Sajid Javid revealed that the number of potential Windrush cases reported to a dedicated Home Office taskforce had reached 3,000.
More than 100 people have had their cases processed and now have the documents they need, Mr Javid told MPs on Wednesday.