The move follows a decision by the Department for Transport to permit an expansion in passenger numbers to up to 50% of a ship’s capacity, provided guests are fully vaccinated.

Sailings could previously operate with up to 1,000 passengers or 50% capacity, whichever was lower.

In a statement announcing its policy change, MSC said its focus was “on inconveniencing as few guests as possible in this rapidly changing environment".

“It will, however, understandably frustrate a number of our guests who had already booked their holiday with us for voyages but are not yet fully vaccinated,” the line said.

“While we regret that this change to the capacity limits will disrupt their travel plans and our ability to accommodate some guests as originally planned, the capacity increase allows us to protect many more guests’ holidays which would have been otherwise affected by the recently announced delay of the easing of Covid restrictions.

“We are now contacting affected guests to offer them options for their holiday, including rescheduling, refunds and exemptions.”