BRITTANY Ferries has announced plans to operate a once-a-week winter ferry service from Portsmouth to Santander from next January. It temporarily replaces the Plymouth-Santander run and is being launched as the rival P & O European Ferries is considering a Portsmouth-Bilbao service for next summer.

Brittany Ferries says it has decided to operate all its winter passenger ferry services from Portsmouth. This means there will be no winter Plymouth-Roscoff operation.

The Santander service will return to Plymouth next April for the summer; but from November 1993 it will again depart twice a week, through the winter, from Portsmouth. By operating winter services from Portsmouth, the company believes the Santander service will attract 'mini-cruise' passengers from London and the South-east.

P & O European Ferries has been considering plans to operate from Portsmouth to Bilbao in northern Spain for almost two years. This route was operated 20 years ago by the Swedish Lloyd company, but it was never a commercial success.

Brittany Ferries believed that on the sea route to northern Spain, the 24-hour sailing from Plymouth to Santander was a better commercial proposition than a 28-hour Portsmouth-Bilbao/Santander service. It was right: such was its success with tourists and freight companies that the company recently launched the 27,000-ton superferry Bretagne on the route and will next year add a second ferry.

P & O European Ferries said this week it is still hoping to announce a Portsmouth-Bilbao service from April. 'We are negotiating with the Spanish authorities and we are continuing to look for a ferry to operate the service,' said Ian Todd, for the company. But by running its winter service to Spain from Portsmouth, Brittany Ferries clearly hopes to kill off the P & O plan.

With the Channel tunnel due to open at the end of next year, P & O is keen to develop its business on the western Channel - and northern Spain is the destination with the biggest commercial potential.

P & O European Ferries estimates it will carry 14 million passengers this year - its third record year of cross-Channel traffic. 'Instead of having one long continental holiday a year, we believe more people are taking as many as three short trips,' said a company spokesman.