Colin Firth was left baffled by Woody Allen's lack of direction on the set of new period drama Magic In The Moonlight, because the revered filmmaker often insisted the British actor should do "whatever" he wanted.

The King's Speech star portrays a cynical 1920s illusionist who is hired to expose Emma Stone's fortune teller character as a fake during a week-long holiday in the South of France.

His part required him to perform a number of soliloquies, but Firth admits he really had no idea what he was doing during certain scenes as Allen's method of filmmaking at times involved very little instruction.

Recalling one scene, in which his character Stanley recites a prayer to God, he explains, "In this case (of the soliloquy), there really is nobody else (in the scene) but the all-seeing eye of the director, who, if he is happy, you just hear the sound of the crew packing up and going off to shoot something else...!

"If he wanted to be very specific about something, you'd hear a lot from him. And sometimes he'd just say, 'Do whatever, you know, whatever you want. If you wanna change it...'.

"Well, I didn't know what I wanted most of the time, I just wanted to know what he wanted! I would do something and then he would just (say), 'That's not it', or he might come up and say, 'That was funny, if only to me...'"