Britain’s ferry firms say they have not been told of a government ruling that UK-bound travellers lose quarantine exemption if they sail back from France or the Netherlands.
Both countries were removed from the list of exempt nations on Saturday.
British holidaymakers driving back from countries such as Germany, Switzerland and Italy can avoid the need to self-isolate for 14 days if they drive straight through a “high-risk” country such as France, Belgium or the Netherlands.
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Quarantine-free transit is allowed for cars only if the driver and passengers do not mix with others during the journey. For example, they must not stop for a meal or drink.
Some motorists had hoped that driving straight through from Germany and boarding a ferry at a French or Dutch port immediately would save them having to self-isolate on return to the UK.
But the Department for Transport (DfT) has told The Independent that because the occupants of a car must leave the vehicle before sailing – for safety reasons – they are deemed to have mixed with others while the ship is tied up in a French or Dutch port.
They are therefore liable for 14 days of self-isolation on arrival in the UK.
In contrast, Eurotunnel customers can claim exemption, so long as they follow the transit rules while passing through France and any other “no-go” nation, such as Belgium or Luxembourg.
Abby Penlington, marketing director of Discover Ferries, said: “The government has not made the ferry industry aware of this, and if it is the case, it is confusing for passengers and would put the ferry industry and Eurotunnel on different playing fields.
“As such, we will be seeking urgent clarification from the Department of Transport and Foreign Office.”
Eurotunnel even says that pet owners, who are required to attend an office in the Calais terminal, retain exemption because the encounter takes place after passing through UK frontier formalities – which are “transposed” to France.
Vincent, in the social media team for the company’s Shuttle operation, tweeted: “Good news, the pet reception office is considered as border controls so if you come from a country not involving quarantine and you have just drove thru without stopping in a country which is on the list you are then exempt of self isolating.”
The two optimal German locations for UK-bound Eurotunnel travellers to refuel are the city of Aachen and the town of Perl – just across from the village of Schengen in Luxembourg.
Calais is three hours and 30 minutes’ drive from Aachen, an hour longer from Perl.
Meanwhile Brittany Ferries has urged the French government to drop its plan to introduce a tit-for-tat quarantine for arrivals from the UK.
The French ferry firm normally carries 2.6 million passengers each year, of whom 85 per cent are British.
The director general of Brittany Ferries, Christophe Mathieu, said: “This has already been a disastrous summer season for us and all the businesses in northwest France that rely on the friendly British invasion each summer.
“If such [quarantine] measures are implemented it would be an exercise in self-harm for France plc, damaging our business, as well as those of thousands of others in the regions we serve.”
The DfT has also confirmed that passengers using Basel airport, serving Switzerland’s third-largest city, must self-isolate for a fortnight on return to the UK.
The airport is located inside French territory, two miles from the Swiss border, and is connected by a route douaniere (“customs road”). But because it is in France, the quarantine rules apply.