“Perfect girl” Prunella Stack, who blazed a trail for women’s health and fitness, died yesterday at the age of 96.

A driving force behind the growth of the Fitness League, she was still spurring women into keep fit action as recently as two years ago.

Exercising was in her blood after all, as it was her mother who launched the Women’s League of Health and Beauty (WLHB) in 1930, when Ms Stack was 15.

Mary Bagot Stack led a drive for exercise adapted to suit the needs of people of all ages and abilities and taught by trained physicians.

It was one of the first exercise systems conceived in the UK and she promoted it through huge public displays. She believed her daughter’s robust good health, beauty and grace were in no small part due to the exercises and dancing that formed an integral part of her daily life.

Young Stack was upheld as the embodiment of the ideals of her mother’s training and was labelled the “perfect girl” by the press.

It was a description which she apparently had no difficulty in living up to, playing a key part in developing the League into an international organisation.

When her mother died, its future was left in her hands, although she was only 20 years old at the time.

But despite her young age, she threw herself into teaching, performing, and public speaking with skill and charm.

In 1930s Britain, austerity sparked public health fears andled to what is said to be the first ever fitness craze – with Ms Stack a key player in it.

In the days before Lycra gym-wear was a must-have for fitness freaks, black satin pants and white shirts were the uniform of the League, and Ms Stack was pictured wearing both for the public displays and performances in which she was involved.

She also lived a full and eventful private life, outliving three husbands and moving to Africa for a time.

Her first marriage was to Lord David Douglas-Hamilton, who she wedded in Glasgow Cathedral in October 1938, celebrating with a wedding reception attended by hundreds of friends, family and WLHB teachers and members.

But the marriage was a tragically short one: Lord Douglas-Hamilton was killed just six years later while serving with the Royal Air Force during the Second World War.

Ms Stack dealt with her grief by continuing her mother’s work and, after several years spent helping rebuild the League’s membership, which had been severely declined during the war, she remarried.

Her second husband, Alfred Albers, was a surgeon in Cape Town, South Africa, and it was to this city that Ms Stack moved to be with him. But her second marriage was cruelly cut short after even less time than the first, when after nine months of marriage Mr Albers was killed in a climbing accident on the country’s Table Mountain.

Ms Stack stayed in South Africa, however, and continued the work she had already started. She established the League there by opening classes first in the black community and later for white women.

She made the headlines in 1953 by organising a mixed-race team to travel to England for a Coronation display. In 1956 she returned to the UK, where she immediately resumed her work.

Her third marriage was in 1964 to barrister and communications lecturer Brian Power.

The couple lived in London but escaped for breaks at their much-loved cottage in Scotland. Mr Power died in 2008.

Ms Stack’s special interest was in training new teachers and above all encouraging a new generation of women who were able to guide her mother’s work into the future.

Today, Bagot Stack principles are used in classes all over the UK, as well as in Canada, New Zealand and South Africa.

The practice of good posture, balance and strong central control underpins the blend of exercise and dance that makes for energetic classes for people of all ages and abilities.

A mouthpiece for the Fitness League, which the WLHB became, said: “Throughout her life the legacy of the League which her mother left her was always central to (Ms Stack’s) existence and she worked tirelessly to ensure its survival.

“Over the 80 years since the League began, thousands of women have been living proof of the benefits of the training which Mary Bagot Stack devised and which Prunella continued into the new century.

“As she did, they enjoyed high levels of fitness, fun and friendship throughout their lives. Prunella was the perfect girl who became the perfect woman, much loved and admired by all who knew her.”

Ms Stack died at home in south west London, leaving behind two sons, Iain and Dairmid.

Her granddaughter is television presenter and wildlife conservationist Saba Douglas-Hamilton.