Work on a new system to register EU migrants who come to the UK after March 2019 has "barely begun", according to worried Home Office officials.
The department is scrambling to get new systems in place after the prime minister Theresa May said new arrivals would not be automatically entitled to remain in the UK during the transition period.
It is one of the sticking points in negotiations with the European Commission, which is insisting the UK abides by the rules of the single market for the two years after Brexit day.
According to the Times, Home Office officials wanted the government to guarantee that new arrivals would get the same rights as existing EU citizens during the transition, but were rebuffed by Mrs May.
They now have just over a year to design a new system to register not only new arrivals, but also the 3 million EU nationals already in the UK.
Two government sources told the paper that work had "barely begun" on putting together a new system.
“Rightly the focus has been on registering the three million nationals who are already here, and while that has been progressing well there is still a lot of work to do,” one source said.
“But the problem is that this is a streamlined process that doesn’t question whether in future someone might not have the right to work."
The other source was also pessimistic about the prospect of getting a fully functioning new system in place by next spring.
“The way things look at the moment it almost certainly won’t be ready. The government doesn’t have the best record of these kind of projects anyway and the most pressing priority is to ensure that nothing goes wrong with registering existing EU nationals. If that goes wrong it will be a disaster.”
A Home Office spokesman rejected those claims, saying: "The precise details of the implementation period are currently being negotiated with the EU, but planning is well under way.”