The ferry company, which operates the Belfast to Stranraer and Larne to Fleetwood routes, said its latest figures showed significant growth.

Ian Baillie, Stena Line route marketing manager, said leisure travel carryings had increased by 13% in November, year on year.

This means a reversal of a decline which meant a reduction of 5% in passenger volumes and 4% in car traffic in 2005.

Mr Baillie said the November increase equated to 2,000 additional cars being carried on the two routes, and said that across all its Irish Sea routes the upturn was coming out at 15%.

He said: "With more investment and improvements planned for 2008 we expect next year to be even better, with more holidaymakers seeing the benefit of travelling by ferry rather than by air.

"When you think about the hassle and hidden costs associated with flying these days, from airport delays to the so-called low-cost airlines' increased stealth fees on baggage, taxes and add-ons such as priority boarding and airport parking - as well as the recent news that Irish airlines have topped the EU complaints league - it's no wonder travel by sea is being seen as a more attractive option."

Competition has hotted up this autumn with Ryanair launching its service from George Best Belfast City Airport to Glasgow Prestwick.

Meanwhile easyJet and flybe are competing head to head on the routes from Belfast to Edinburgh and Glasgow International.

Stena, which operates both the HSS fast ferry and a slower conventional ferry on its Belfast to Stranraer service, is planning to reduce the journey time.

The first stage of the operation will be a move at the end of May next year to a new £35m base at Victoria Terminal IV, close to the Fortwilliam exit on the M2 and two miles downstream from the existing terminal.

The second phase was to have involved a move from Stranraer to a new £40m terminal at Cairnryan, but that proposal has now been aborted.

In the autumn it was announced that expansion plans at Cairnryan had been halted, due to escalating costs. Port of Cairnryan said that detailed cost projections for the project had proved to be "prohibitive".