Paul McCartney poses for PETA

Sir Paul McCartney decided to become a vegetarian after realising he was a murderer on a fishing trip.

The Beatles legend reveals why he gave up meat on a new poster for animal rights group PETA (People for the Ethical Treatment for Animals), which is emblazoned with the words 'I Am Paul McCartney, And I Am A Vegetarian'.

The advertisement features the singer sitting on a stool wearing a trilby and pointing to the slogan on his T-shirt which reads 'Eat No' over a picture of a cow.

A statement in the right corner of the poster reads: "Many years ago, I was fishing, and as I was reeling in the poor fish, I realised, 'I am killing him - all for the passing pleasure it brings me.'

"Something inside me clicked. I realised, as I watched him fight for breath, that his life was as important to him as mine is to me."

Paul, 65, is the latest in a long line of celebrities to pose for PETA. Alicia Silverstone, Casey Affleck, Forest Whitaker and Joss Stone have all previously fronted campaigns for the organisation.

Paul's late wife Linda McCartney was a strong advocate for animal rights and even launched her own range of vegetarian meals. The couple's fashion designer daughter Stella is also a strict vegetarian and refuses to use any animal products, such as fur or leather, in her clothing lines.