By Nick Assinder
Political Correspondent, BBC News website
She has been out of office for 15 years, there have been two prime ministers and four, soon to be five Tory leaders since that day.
Yet, as she celebrates her 80th birthday, the figure of Margaret Thatcher still looms large over British politics.
Baroness Thatcher served as prime minister between 1979 and 1990
Tony Blair almost glows when he is compared favourably to her and, it is often claimed, no Tory candidate will get a look in with the grassroots party unless they pay due respect to her political memory.
That last is why every one of the current candidates either mentioned her by name or invoked her memory in their campaign speeches at the Blackpool conference.
The bottom line is that, for many Tories, she was simply the greatest leader they have had since Churchill, both personally and politically.
Personally because nobody had ever seen anything quite like this handbag-wielding, unapologetic class warrior before.
And politically because she transformed Britain in a way you either loved or loathed, depending largely on which side of the class war you found yourself on.
Few doubt that she had such an impact on British society - and arguably the world - that whoever came after would be struggling to match it or find another, radical route forward for Britain.
And it is often claimed that, to a greater or lesser extent, we are all Thatcher's children now because she shifted the hub of politics.
Blair is seen as Thatcher's heir
Tony Blair succeeded in coming to power by promising not to tear up all the reforms she delivered but to put a more socially caring face on her Britain.
And, ironically, much of would-be Tory leader David Cameron's attraction is that he would plough that very same furrow.
When his friends call him the heir to Blair, they are also saying that he is a natural heir to Thatcher.
And, whoever takes over from Tory leader Michael Howard in December, they will have more than one eye over their shoulder.