The arrival records for tens of thousands of immigrants from the Windrush Generation have been found in the British National Archives.
The find strengthens the cases for those trying to prove they are British citizens who were being told they had to leave the UK.
The ledger, found after an investigation by the Financial Times, shows arrivals at ports until 1960 with more than 85,000 people arriving from Caribbean countries.
The arrival records include include citizens who arrived from the Caribbean on Empire Windrush in 1948. It was the ship's name that would come to define the generation.
The information, compiled by the Board of Trade, could prove vital in helping those under threat to claim UK citizenship.
The Home Office destroyed its cache of landing slips eight years ago, in a bid to up data protection.
But the department has since rejected applications for UK citizenship because of a lack of evidence to support their arrival date claims.
The move came despite staff warnings that the move would make it harder to check the records of older Caribbean-born residents experiencing residency difficulties, it was claimed.
The revelations come after Prime Minister Theresa May issued her second apology in two days to the Caribbean migrants threatened with deportation.