Eurotunnel has warned customers hoping to beat the government's latest travel quarantine deadline not to just turn up at its terminal on Friday.
People coming to the UK from France and the Netherlands will be forced to quarantine for 14 days if they arrive back after 04:00 on Saturday.
The firm warned hopeful passengers: "Do not turn up unless you have a booking. You won't get on a crossing."
"This being a peak August weekend, we are already full up with bookings."
John Keefe, director of public affairs at Getlink, which operates the Channel Tunnel, told the BBC: "The service is already very busy this weekend and there is no additional capacity."