Margaret Thatcher began plotting to defeat the coal miners from the day she took office, according to her official biography published today.

The new prime minister put her deputy, Willie Whitelaw, in charge of the preparations for a showdown with the National Union of Mineworkers (NUM).

However, she was forced to postpone the confrontation until her second term of office after warnings that she was not in a strong enough position to win.

The details are disclosed in Margaret Thatcher, The Authorised Biography – Volume One: Not For Turning, by former Daily Telegraph editor, Charles Moore.

Mr Moore was given full access to all her personal and Government papers as well as interviewing her, her family and those who worked most closely with her.

According to the book, when she entered office in May 1979, she was determined to avenge the defeat of Edward Heath's Conservative government, which was brought down by the NUM five years earlier.

"She summoned Willie Whitelaw and Sir Robert Wade-Gery, the Deputy Secretary to the Cabinet, and announced: 'The last Conservative government was destroyed by the miners' strike, and we'll win. And you, Willie, will do it'," Mr Moore wrote.

However, the showdown with the NUM had to await Thatcher's second term following her 1983 general election victory.