The increase represents an additional 5,000 cars, in a year when the overall number of cars carried between the UK and Continental Europe remained static.

It means that Stena, which introduced two new superferries on the route in 2010, has now grown its North Sea car volumes four years running, to a total of 105,000.

Coach traffic grew even faster, by 13.7%, and Stena’s total passenger numbers from Harwich were constant at above 500,000, in line with the wider market.

Lars Olsson, Stena Line’s general manager for travel on the North Sea, said: “The success of Stena Line’s North Sea operations in 2011 is particularly impressive given the challenging context both for the ferry industry and the UK travel industry as a whole.

“We are pleased to have grown our car and coach traffic to Holland and sustained overall passenger numbers during a difficult year. It’s particularly important for Stena Line to have been successful in 2011 after having invested over �375m on new Superferries the previous year.

“We’re attributing some of the growth to an increase in large groups who are avoiding the high air passenger duty tax on UK flights.

“There have also been growing numbers of business and leisure passengers from East Anglia and London, using our overnight crossings for short trips where they get to travel in comfort whilst they sleep and take advantage of our wine and coffee bars, choice of restaurants, free WiFi, dedicated areas for children and teenagers and nine types of cabin.”

He added: “Stena Line expects a strong 2012 on the North Sea despite the ongoing challenging market conditions, notably thanks to outbound demand fuelled by large-scale Dutch events such as the return of Floriade, the 10-yearly international flower exhibition, and inbound demand stimulated by the Olympics.”