Dame Helen Mirren has revealed when Steven Spielberg rang to ask her to star in The Hundred-Foot Journey she thought it was a prank call.

The 69-year-old actress stars as Madame Mallory in the big screen adaptation of Richard C Morais's best-selling book about the rivalry between an Indian family and a French chef, after the family open an Indian restaurant 100 feet across the street from a Michelin-starred French eaterie.

The film is directed by Swedish filmmaker Lasse Hallstrom, who directed Chocolat and Salmon Fishing In The Yemen and produced by Spielberg and Oprah Winfrey.

Dame Helen revealed: "It was that classic phone call of, 'It's Steven Spielberg on the line for you'. And whenever an actor is lucky enough to receive that phone call, you never believe it and think someone's having you on."

Director Lasse encourages improvisation, which the veteran actress admitted she found a little intimidating.

She said: "He warned me at the start of the shoot that he'll probably change things around and ask me to improvise.

"He said, 'I like to keep things loose', and it was very true. He'd get an idea and suddenly go for it, so you felt you were never in a prepared rut that you had to follow. Sometimes that was frightening, because you felt wrong-footed, but it was always exciting."

Dame Helen revealed there was a time when she felt the same way about acting, "but I really don't so much any more," she reflected.

"I love my profession, don't get me wrong, and I'm very committed. But I'm not obsessed the way I used to be, especially as a very young actress. It was a church for me, my religion."

:: The Hundred-Foot Journey is in cinemas now.