Sir David Attenborough said Britain's new polar research ship which bears his name could be key to preserving the planet as he launched it for the first time.

The veteran broadcaster pushed the button at the Cammel Laird shipyard in Birkenhead on Saturday to allow half of the 10,000-tonne vessel to slip into the River Mersey.

The 92-year-old said it was an "extraordinarily emotional moment" as the £200 million ship, named the RRS Sir David Attenborough, entered the water.

The vessel, which received more than 124,000 votes by the public to be called "Boaty McBoatface" in an online poll, is the most technically advanced survey ship ever built and will accommodate 60 scientists on research trips to Antarctica when completed.