Margaret Thatcher, whose celebrations to mark the 20th anniversary of her becoming Britain's first woman prime minister began on Tuesday evening, will go down in history as the woman who rescued the country from oblivion.

Sir Bernard Ingham: For years, his master's voice

In the process, she astonished and delighted even her supporters. She still shocks and dismays her opponents, not least because Labour leader Tony Blair has appropriated her approach.

The source of these emotions lies in the Britain she inherited in 1979. For years it had struggled - and latterly failed miserably - to reconcile full employment with low inflation as continual union disruption further undermined its economic performance.

The so-called Winter of Discontent of 1978-79 left many wondering whether Britain was still governable.

She had resolved in opposition to break with the past, stop the trend towards a corporate state in which the unions effectively had a veto and to liberate the country through a rigorous philosophy which came to be known as Thatcherism.

The cure was fierce as unemployment soared above three million and manufacturing industry was decimated.

Her first two years were not merely a battle with her opponents and against public scepticism, which expected her to U-turn "like the rest", but also with those within her own Cabinet who feared the social and political consequences of her treatment.

Ronald Reagan and Margaret Thatcher forged a special relationship

With a bravura display of raw courage, conviction, strength of character and iron will, she saw the lot of them off and eventually - after five or six years - was rewarded as prime minister with a resurgent industry and enterprise, new jobs, inflation, spending and unions under control, national debt being repaid, a vast privatisation of industries and services and a new respect for Britain in the world.

In between she recovered the Falkland Islands from the Argentine invader with a remarkable feat of arms in which she provided the political direction while her military got on with the campaign.

She forged an intensely loyal but frank alliance with President Reagan which brought something genuinely special to the Anglo-American relationship and struck up a remarkable friendship with Mikhail Gorbachev, an atypical Russian leader.

She fell celebrating the end of the Cold War in 1990 to a messy panic in her party which still affects its morale.

The "Iron Lady" can celebrate the 20th anniversary of her rise to power

Her demise was partly due to her own and her party's profound unhappiness about the European Union's integration.

The issue contributed to the government's economic problems and progressively robbed her of leading Europhile ministers.

But it did not prevent her from becoming a powerful international figure who massively raise Britain's reputation in the world.

She succeeded because of her clarity and strength of purpose, her physical and mental stamina and the domestic security provided by her immensely loyal husband, Denis.

Above all, the Iron Lady had iron will. Without it, there would be no celebrations today.