The company said that the changes to its schedule came after a weekend over which 35,000 passengers either cancelled or delayed their plans to sail.
The UK announced that France was back on its quarantine list on August 13.
Two ships - the Armorique and the Bretagne - will be laid up completely, while the Etretat will also not resume crossings.
The changes are as follows:
- Plymouth to Roscoff: Brittany Ferries ship Armorique will be laid up from August 31. Brittany Ferries ship Pont-Aven will replace Armorique on the Plymouth to Roscoff route from September 10, with three return trips per week.
- Portsmouth to St Malo: Brittany Ferries ship Bretagne will be laid up from September 7.
- Portsmouth to Cherbourg and Le Havre: The ship Connemara will continue to operate the Cherbourg and Le Havre rotations from Portsmouth, but will no longer serve Spain.
- Plymouth to Santander: The ship Brittany Ferries Pont-Aven will continue to operate one return sailing from Plymouth to Santander during the week
- Cork to Roscoff: The ship Brittany Ferries Pont-Aven will continue to operate one return sailing during the week
- Brittany Ferries ship Etretat will not resume crossings, as planned.
In a press release, director general of Brittany Ferries, Christophe Mathieu, said: “We warned over the weekend that schedule changes were likely, as quarantine measures have led to a significant drop in demand for our services.
“This is not something we want to do. However, in the context of a terrible summer season we have no choice but to consolidate sailings that, by virtue of lack of passenger numbers, are uneconomic to run.
“These extraordinary decisions are regrettable and we apologise in advance to all those whose travel plans will be disrupted.”
The company added: “[We] will do all we can to accommodate displaced customers on other services. The call centre is expected to be very busy in the days ahead. Passengers are therefore asked to wait for notification of any change to their booking and – where possible – to make alternative arrangements via the My Booking facility on the [Brittany Ferries] website.”
Quarantine changes a ‘sledgehammer blow’
The schedule changes come after Mr Mathieu said that the quarantine rules were a “sledgehammer blow” to its operations, which “may not survive” the rest of the season as a result.
Speaking to news service FranceInfo, Mr Mathieu said: “This is a sledgehammer blow. We already did not have enough passenger activity in the months of April, May or June. This weekend we were supposed to transport 5,400 passengers between England and France. Now, we will only transport 2,300.
“To give you an idea [of the problem], last year, for the same weekend, we transported 13,400. We thought that we would already be on 40% of the season [norm], but now the season will end with at least half of these reservations.”
Mr Mathieu said that the effects were likely to impact the business until at least Spring 2021.
'No reciprocal quarantine'
It added that it was “lobbying hard” to ask the French Government to drop its plans for a “reciprocal quarantine”.
Mr Mathieu said: “If France announces that British people need to self-isolate or quarantine when they arrive in France, then we fear that the entirety of our bookings will disappear.”
The company has also said that it is “nonsense” that exemptions existed to the quarantine for people travelling through the Eurotunnel after transiting in France - for example, by driving through France without stopping - but that such exemptions did not apply to those arriving in the UK on a ferry, even if they too did not stay or interact with others in France beforehand.
Brittany Ferries said it has sought "urgent clarification" from the Government over the ruling, and branded it "a nonsense" that puts us [ferries] "at a disadvantage for no apparent reason”.
The UK quarantine rules now apply to all four European countries currently served by ferry to and from the UK: France, Belgium, the Netherlands and Spain.