Lord Dobbs, a former adviser to Baroness Thatcher, described her as Britain's "finest 20th century peacetime prime minister".

"She became the 20th century's finest peacetime prime minister," he said.

"She will have accolades showered upon her and she will also have much criticism that will follow her but that is the thing of greatness.

"She decided to do what she was thought was right rather than what she thought was necessarily popular."

Lord Dobbs was with the then Mrs Thatcher when she achieved her first election victory.

He said: "I was the first one to be able to tell her on election night in 1979 that she had become prime minister.

"I was a very small part of what became a huge change in history - it was extraordinary to be a spectator of history at that time."

The peer was also present at some of the more painful moments for the first woman prime minister.

He said: "I remember her at the Brighton Bombing and the extraordinary resilience in the hours after the attempt to kill her when several of her friends had been killed.

"I will always remember her being literally dragged out of Downing Street - a Shakespearean tragedy almost leaving the fingernails in the carpet of Downing Street - and the tears we all saw.

"Margaret had an extraordinary ability to embrace very closely those around her. She could be very caring and very compassionate and not the side we often remember publicly.

"It is essential to remember about her that she was a very complex character and simply the two-dimensional character of the woman made out of steel that some people tried to portray her as.

"She could be that when she needed to be but she was much more than that."

Lord Dobbs, who wrote the House of Cards series of books, paid tribute to Lady Thatcher from his home near Warminster in Wiltshire.

"Great leaders are often made by great crises," he said.

"I don't think anybody in 1975 or 1976 would have spotted in her that extraordinary 'Iron Lady' that she was later to become.

"She showed her resilience through many ordeals - the invasion of the Falklands, many thought we couldn't beat the miners, the extremists, the Scargills, the militants because other prime ministers had tried and failed abjectly.

"She took on those things that people said were impossible and she had the extraordinary ability in succeeding.

"She ended in failure in the sense that she was eventually dragged from office.

"The whole Poll Tax episode was a disaster and I think showed she had lost her sensitivity by then.

"But looking back on her career as a whole she did things that many people thought were impossible and most people could simply not have envisaged and that I think will make her role in history.

"She took a country that was deeply flawed and very badly damaged - the sick man of Europe - and she made it strong again.

"And for that, whatever our political persuasions, we owe her a huge debt of thanks."