Baroness Thatcher will never make a public speech again after suffering "a number of small strokes" over recent months, her office announced yesterday. Doctors have told the former Conservative Prime Minister that these strokes can neither be predicted nor prevented.

And Lady Thatcher, 76, has "with great regret" decided to abide by their advice, which includes cutting back her programme "at once".

The doctors have told her that, in particular, she should avoid the undue strains of public speaking. Last night, she was resting at her London home.

Lady Thatcher had been due to make five trips to the US this year fulfilling lecturing engagements.

She was also busily engaged in promoting her new book Statecraft.

The announcement follows what was believed to be a stroke suffered by Lady Thatcher on Tuesday.

Last night, Iain Duncan Smith, the Conservative leader, said: "I am saddened by the news that Baroness Thatcher is unwell and fully understand the reasons that she has been advised to withdraw from her public engagements."

Former Tory chairman Lord Tebbit said he had been concerned about her health for some time.

But he insisted she was "still very alive" and it would not be the last people had heard from her.

Former Conservative Chancellor Lord Lamont said: "I am overwhelmingly sad at this news. Margaret Thatcher is usually right on the big issues, and the louder the noise against her, the more right she usually is."

Former Labour deputy leader Roy Hattersley described Lady Thatcher as the "Paul Gascoigne of politics".

"She was a great figure, she's still about, she comes on to play from time to time and everybody writes about it, but she doesn't make any difference to the game," he said.

"I don't think she's been influencing the game of politics for five, six, seven years."