Diane Abbott has warned halting free movement of people the day after a no-deal Brexit would “create chaos” and “make Windrush look like a minor blip”.
Downing Street announced yesterday that the system allowing European Union citizens to freely live and work in the UK would include tougher criminality checks for people entering the country.
But Labour's shadow home secretary has warned that an abrupt change to the system could have severe consequences.
The so-called Windrush scandal involved thousands of immigrants who arrived in Britain legally being wrongly threatened with deportation.
Ms Abbott told BBC Radio 4's Today programme: "There are currently three million here altogether; a million have registered for settled status, there's no possibility of two million registering between now and the 31st October, and then those EU nationals that were here but haven't registered for settled status will be in the exact same position as the Windrush people.
"The way Boris is doing it is heading to a catastrophe - it will make Windrush look like a minor blip."
A Downing Street spokeswoman insisted the process to apply for settled status would not change and the two million EU citizens yet to apply would not be prevented from entering the UK after free movement ends, and that EU citizens resident in the UK would not be prevented from re-entering after a trip abroad.