Travellers trying to return from France on Friday to avoid the quarantine restrictions face a scramble for tickets costing hundreds of pounds.
British Airways was charging £452 for a direct flight from Paris to London Heathrow on Friday night, but the plane was fully booked by 10.30am.
The same journey on Saturday can be made with the airline for just £66.
The cheapest ticket on a Eurostar train from Paris to London is £210, compared with £165 on Saturday.
Car-carrying Channel Tunnel trains are fully booked until Saturday, which is too late to avoid the quarantine.
A spokesman for Eurotunnel Le Shuttle said: “Due to the recent Government announcement, our shuttles are now fully booked until tomorrow morning.
“There is no more ticket availability and we are not selling tickets at check-in. Please do not arrive at the terminal unless you have a ticket valid for travel today.”
P&O Ferries has limited availability, but one person travelling with a car from Calais to Dover can buy a ticket for £200.
Travellers in the south of France face a struggle getting back to the UK before the 4am Saturday quarantine deadline.
Many direct flights to the UK on Friday are sold out.
Flight booking website Skyscanner suggested there were no direct flights from Biarritz to London.
The cheapest option it offered was to take one flight to Paris, another to Belfast and a third arriving at London Stansted shortly before midnight, at a total cost of £284.
The lowest priced ticket involving just two flights is £579 with Air France, changing in Paris.
Travellers trying to return from the Netherlands to the UK before quarantine restrictions are imposed also faced difficulties.
All easyJet flights from Amsterdam to London were sold out.
The cheapest fares offered by British Airways for travel on the route on Friday are £327, compared with £128 on Saturday.