Sir Peter Shaffer, the Oscar-winning playwright whose work included Equus and Amadeus, has died aged 90.

In a statement, his agent, Rupert Lord, said he was travelling in Ireland when he fell seriously ill and died with his niece Cressida by his side.

Sir Peter won a best adapted screenplay Oscar for Amadeus, his play about the life of Mozart seen through the eyes of bitter rival, composer Salieri.

The 1977 film of Equus was nominated for three Academy Awards.

In a tribute, Rufus Norris, the director of the National Theatre, said: "Peter Shaffer was one of the great writers of his generation and the National Theatre was enormously lucky to have had such a fruitful and creative relationship with him. The plays he leaves behind are an enduring legacy."

Sir Peter was born in Liverpool, the identical twin of playwright Anthony Shaffer, with whom he collaborated on early novels, which they published under the joint name of Peter Anthony Shaffer.

The sons of a property company director, they moved with their parents from Liverpool to London in 1935 and were educated at St Paul’s School.

From national service as “Bevin boys” working in Kent coal mines from 1944 to 1947, they both went to Cambridge, co-editing the undergraduate literary magazine Granta.

A revival of Amadeus is duo to be staged at the National Theatre in October.