Keira Knightley's mother attacks weight critics

She said that her daughter never had to diet but instead followed a special eating plan - high in protein and carbohydrates - to keep weight on.

Miss Macdonald, 57, claimed the actress must 'eat like a horse' to keep herself at a healthy weight.

She said: 'She has always been thin. She's her daddy's daughter, with his long body.'

The playwright explained that Miss Knightley was given an eating plan to bulk up for the role of Queen Guinevere in 2004 film King Arthur.

However, the plan called for her to eat less than she normally did and had to be abandoned after she lost weight.

The result was that posters intended for the U.S. market showed Miss Knightley with a digitally-boosted bust.

Her mother added: 'It's a playground situation that we're looking at with the Press - it's a form of bullying - but what can we do?'

Image WENN