Brittany Ferries was forced to divert its flagship vessel to a port in northern France last night after it was hit by a freak wave that smashed a cabin window and flooded several cabins.

The 41,000-tonne Pont-Aven was sailing from Plymouth to the Spanish port of Santander through a force nine gale when it was hit by a wave thought to be 40ft high.

Most of the 1,149 passengers on the ship, which has 11 decks, were in the ship's restaurant or bar when the wave hit at 10.32pm. Britanny Ferries said the wave broke the window of an unoccupied cabin on deck six.

Stephen Tuckwell, a Brittany Ferries spokesman, said that five passengers and one crew member were treated by the ship doctors for minor injuries. "It was mostly bruising, the worst was a sprained ankle." he said. "They were knocked over as the wave hit."

The ship was passing Ouessant on the northwestern corner of France when the wave hit and was diverted to Roscoff, where she arrived at 5am local time this morning. Most of the passengers had their cars on the ferry and decided to carry on by road, but some preferred to return to the UK.

Mr Tuckwell said the wave was exceptional. "It's the first time in recent memory that it's happened. I certainly can't recall it happening before," he said.

Brittany Ferries said that the £100 million ferry was to sail to Brest for repairs but the company expected it back in service by the end of the week. The ferry, built in 2004, can take 650 cars and up to 2,400 passengers.

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