Good news, ladies — Joan Collins has revealed the secret to maintaining a perfect hourglass figure into your 70s.

The bad news? It’s spending your entire life on a diet.

Collins has told how she went from one punishing regime to another throughout her acting career, trying to please directors who said she was too fat.

She even claimed she was once prescribed the amphetamine speed to help her lose weight for a film role.

The 79-year-old made the comments at the launch of her one-woman show, One Night With Joan, in Northampton on Saturday.

Miss Collins is best known for playing scheming Alexis Carrington in ‘Dynasty’, but hasn’t acted since 2010.

She said: “The added incentive about not acting nowadays is not having to diet any more. Your hips always had to look slimmer, your face thinner. As an actress, you are always on a diet when working.

“I was told to take speed to help get the weight off. At times, I was told I wouldn’t even get work because I was too fat.”

Collins said Hollywood casting directors always used to insist that she lost weight before giving her a part.

Tomatoes, cottage cheese

She said: “As soon as they saw me in the flesh, they insisted I go on a diet and exercise every day. It was tomatoes and cottage cheese, lettuce and cottage cheese and cottage cheese and cottage cheese.

“I was told I needed to lose eight pounds [3.6kg] from my nine stone immediately. But I cheated and my doctor put me on a series of little green slimming pills which did work.

“I lost eight pounds in two weeks and two weeks’ sleep, because I finally found out those little green pills contained speed.”

Collins made her film debut in 1951, and became a magazine pin-up in the ’50s and ’60s.

The actress has been married to her fifth husband, 47-year-old theatre producer Percy Gibson for 11 years.

In 1960, she screen-tested for the role of Cleopatra, but lost out to Elizabeth Taylor.

Hard to bag roles

Collins, who has three children and three grandchildren, admitted that she had found it increasingly difficult to win film roles as she grew older.

She said: “In Hollywood, you’ve flowered in your 20s, peaked in your 30s and it is rare for an actress to be a leading lady in her 40s and rarer still in her 50s.

“After that, it is character parts if you’re lucky. After 60, a woman is like Africa. Everyone knows where it is but nobody wants to go there.”

But Collins has clearly been making the most of her freedom after so many years of dieting.

Last year, she starred in an advert for Snickers with fellow ‘Dynasty’ star Stephanie Beacham — and it appears she’s a fan of the chocolate bars in real life too.

She said: “I relax by lying in bed with the TV on, with a lot of magazines and a box of Snickers and just chill, and watch old movies and Downton Abbey.”