She has a figure many women half her age would envy.

But Liz Hurley has revealed the trials she has had to endure to regain her svelte form since giving birth to her son Damian.

Asked about her secret at a fashion launch in London, the model-turnedactress, who is 40 in June, said a disciplined diet of only one full meal a day had been the key.

'Eating very little breakfast, not too much more lunch,' she said. 'Then only tiny little snacks in the day.

'But really boring snacks like a banana or six raisins. The only meal I have is dinner.'

Miss Hurley said the regime had enabled her to shed almost four stone in the two years since having Damian, although she admitted it had not been an altogether enjoyable experience. 'It's horrible if you have to lose a lot of weight,' she said. 'I remember thinking I had done so well and thinking "I look so thin again" - and when I weighed myself I was still 25lb overweight. That was a really depressing moment.'

Miss Hurley, who says she now weighs seven and a half stone, said she shunned fashionable regimens such as the low-carbohydrate Atkins diet in favour of simple restraint.

'I'm on a good old-fashioned low calorie diet - I'm going to bed hungry,' she admitted.

But nutritionists voiced concern over the star's long-term health.

Roz Kadir, who has worked with the England rugby team, said: 'She is on a starvation regime, which is extremely unhealthy. I've worked with and advised a number of top models, but she's basically running on empty, which will affect every function of her body.

'Anyone eating that restricted a diet will be severely malnourished.'

Nutrition expert Fiona Phillips questioned the wisdom of embarking on such a radical diet while bringing up her son, by her former lover, millionaire Steve Bing.

'Although I'm sure she doesn't look after the baby much anyway, eating so little will leave her lacking energy,' she said.

'Anyone with experience of a toddler will tell you that you need a lot of energy.'

But any such concerns are evidently far from the mind of Miss Hurley, who revealed she was considering trying for another child with her boyfriend, Indian businessman Arun Nayar.

'I'm sure Damian would like someone to play with,' she added.

Miss Hurley, who dated Four Weddings And A Funeral star Hugh Grant for 13 years, has been with the textile magnate for nearly two years.

When asked about rumours that they were engaged Miss Hurley refused to comment, while Mr Nayar replied meekly: 'I'd better not say anything, I'll only get in trouble.'

However, any nuptials would be delayed by Mr Nayar's current situation.

The 40-year-old is still married to his first wife, Italian socialite Valentina Pedroni, and complex Italian laws would draw out any divorce proceedings into next year at best.