THOUGH her life has ended at the great age of 91 with tantalising thoughts of what might have been -- when once she was widely regarded as the politician destined to be Britain's first woman prime minister -- Barbara Castle nonetheless departs the political stage as a colossus who achieved so much.

Her considerable legacy has left a lasting mark on British life and its social history. She was the woman who made the country's roads immensely safer when as Transport Minister she introduced the breathalyser test to combat drinking and driving -- a step that has made it completely unacceptable today.

Millions of women and their children have her to thank for the introduction of Child Benefit -- a measure that has not only since helped in the upbringing of two generations, but also gave countless mothers financial support and independence in managing the family budget.

She introduced equal pay for women doing the same job as men, which not only ended decades of unfairness, but also gave countless women the confidence to seek better and more-rewarding careers.

The greatest irony, however, was her seeing a Labour government swept to power five years ago on the strength of determination to curb overweening trade union power and influence -- when the much milder proposals she had mooted while employment minister in the 1970s to free Britain from industrial unrest were to prove her undoing.

Nonetheless, as a Cabinet Minister four times over and a creator of legislation that was both true to old-style socialism and the betterment of people's lives -- a goal she lived up to even in her last years as she fought tirelessly for the restoration of the link of retirement pensions with wage levels -- there is no denying her tremendous political impact.

She spanned more than 50 years as a star of the Labour movement and from 1945 to 1979 as Blackburn's MP never let high office get in the way of her role of giving total commitment to her constituency work. Her energy was phenomenal.

So, too, was her presence -- clever, brave, brilliant on the platform and a battling old-style, undiluted socialist, she had all the talent and charisma to have been an unforgettable Prime Minister and will be remembered as the woman who might have been.