The Hollywood hype machine is going into full swing over the $70m production, which opens in the US on 19 May, and in the UK on 16 July.

But McGregor - who plays a young Obi-Wan Kenobi - told The Express newspaper: "Quite honestly, after my initial excitement, the film-making process turned out to be the epitome of tedium.

"The work was so complex with all the special effects and stuff that I found myself hanging around for days. What bothered me most was that everything was so deliberate.

"There was no spontaneity. Your job, as an actor, was just to get it out. I was frowning a lot. It just became a frowning exercise."

Signing up until 2005

McGregor steps into Sir Alec Guinness's shoes

But he says he thinks he did "a good job", and that he has signed up for the film's other two prequels, adding: "I'm just an actor who can't say no. Besides, there's nothing cooler than being a Jedi knight."

The deal commits McGregor - who was six when Sir Alec Guinness played Obi-Wan Kenobi in 1977's original Star Wars - to working with director George Lucas until 2005.

McGregor's uncle, Denis Lawson, played Wedge, the fighter pilot who saved Luke Skywalker's life in the original trilogy.

Star Wars Episode I - The Phantom Menace follows the early life of the evil Darth Vader. Hundreds of British-based fans are planning to fly to the US to see the film as soon as it is released.

Meanwhile, George Lucas has said "everything is well in hand" to meet the 19 May release date, and he intends to start work on Episode II in January 2000.