Brave Gail holds head up high at TV promo

The Edinburgh-born presenter surprised guests at a fashion show thrown to promote her new television series by arriving with the dramatic new look.

She took to the catwalk and paraded confidently alongside a number of stunning professional models.

It is understood the 34-year-old - whose nude picture was famously beamed on to the side of the Houses of Parliament - woke up around ten days ago to discover huge clumps of hair lying in her bed.

She went to visit a doctor who diagnosed alopecia.

Ms Porter is understood to have cancelled her public appearances and considered abandoning plans to travel to Los Angeles for her new show.

But now the presenter, who described in April how coming off Prozac without telling her doctor almost killed her, decided to battle on.

She received a rapturous ovation from the 500 guests who arrived at London's Cumberland Hotel for a party to launch Miss Porter's forthcoming programme Dead Famous Lives, which will air on satellite entertainment channel Living TV in November.

Alopecia is a disease where the immune system mistakenly attacks the hair follicles, the tiny cup-shaped structures from which hairs grow. This can lead to hair loss on the scalp and elsewhere.

Scientists do not know exactly why the hair follicles undergo these changes, but they suspect that a combination of genes may predispose some people to the disease.

In those who are genetically predisposed, a virus or something in the person's environment can trigger such an attack.

But the stem cells that continually supply the follicle with new cells do not seem to be targeted, according to scientists, leaving sufferers with the possibility that their hair may return.

Ms Porter, who went to Portobello High School, shot to fame as a presenter of Top of the Pops and other television shows, with a series of revealing photo shoots in glossy "lads'" magazines significantly boosting her profile.

She married Toploader guitarist Dan Hipgrave in 2001, but the couple recently split up. Ms Porter, though is said to have found happiness with a new partner, cameraman James Lloyd.

Dr Nigel Hunt, a psychologist who researches the stressful effects of alopecia, said: "The causes can be both physical and psychological, and the hair loss can be slight or severe, temporary or permanent. Although is neither life-threatening nor painful, it can have a traumatic effect on your life."

"You might experience embarrassment over your appearance and problems in your relationships with family and friends.

"You might also believe that your job prospects are affected."