A coronavirus testing centre in Kent has been closed to make way for a lorry park for post-Brexit customs checks.
The government is planning to use the land at Ebbsfleet International station if the UK leaves the EU without a deal on 31 December, according to the Local Democracy Reporting Service.
One councillor said local infrastructure "cannot cope" and there would be chaos on the M25.
A Cabinet Office spokesman said no final decision has yet been made.
In July the government pledged £470m on new border infrastructure, which included, if necessary, building additional inland sites across the country where checks can take place.
The spokesman added: "Final decisions on inland sites will not be made until we have established the extent of new infrastructure that will be delivered at ports."
However a leaked Kent County Council letter says: "We have also been notified that the Ebbsfleet testing centre has closed, as the site is required by HMRC for EU exit."
Dartford Labour councillor Sacha Gosine said: "The infrastructure at Ebbsfleet cannot cope with lorries."
He said it would be a "logistical nightmare" for officials.
Closed 'out of the blue'
In September 2019 planning permission was granted to allow use of the Ebbsfleet site temporarily for customs clearance until the end of this year.
Work had started at one of the car parks at the station but this was put on hold because of the coronavirus pandemic.
Ebbsfleet station was then used as a Covid testing site with a capacity for about 2,000 tests a day, but earlier this month testing staff were told "out of the blue" that the site would be closing.
A new coronavirus testing centre has opened in Rochester.
According to the Cabinet Office regional testing sites like Ebbsfleet "were set up at great speed" but the relocation will allow the network "to continue operating as long as needed".
The government's testing system has faced criticism in recent weeks.
An increase in demand for coronavirus tests has led to local shortages - with some people being directed to test sites hundreds of miles from their homes.
The home secretary Priti Patel has defended the system, saying capacity was increasing.
A Cabinet Office spokesman said: "Final decisions on inland sites will not be made until we have established the extent of new infrastructure that will be delivered at ports."