Speaking on the Jonathan Ross BBC chat show this weekend, she said: "When I finished one chapter near the end I absolutely howled."

She also revealed the character of Harry was "totally imaginary" and not based on anyone else, while Ron Weasley was a lot like her oldest friend Sean.

She was in an Edinburgh hotel room alone as she finished writing the book. "I was sobbing my heart out, I downed half a bottle of champagne from the mini bar in one and went home with mascara all over my face, " she said.

When asked if "scar" was the last word in the book as had been reported, she said: "It was so for ages and now it's not. Scar is quite near the end but it's not the last word." She also said it had been a "a hell of an achievement" to keep the cast of all the films British and Irish. Several of the film's stars are Irish, including Brendan Gleeson (Mad Eye Moody), Evanna Lynch (Luna Lovegood), Michael Gambon (Albus Dumbledore) and Fiona Shaw (Petunia Dursley).

Nearly 1.6 million copies of the final Harry Potter book have been pre-ordered online ahead of its release on 21 July. The latest film in the series, The Order of the Phoenix, had its European premiere in London last week. The film opens here on Thursday.