Baroness Thatcher will never make a public speech again on doctors' advice, her office has announced.

The announcement disclosed that she had suffered "a number of small strokes" over recent months, and that doctors had told her that these could neither be predicted nor prevented. The 76-year-old former Conservative prime minister has "with great regret" decided to abide by this advice which includes cutting back her programme "at once".

The doctors had told her that in particular she should avoid the undue strains that public speaking placed on her.

Tory party leader Iain Duncan Smith immediately issued a statement saying he was saddened by the news, but fully understood the reasons that she had been advised to withdraw from her public engagements.

Baroness Thatcher was due to speak at the Swindon Festival of Literature in May.

Festival director Matt Holland said: "We are very sorry in view of the protracted negotiations and the real coup that Baroness Thatcher represented for the festival.

"But of course our thoughts first and foremost go out to Margaret Thatcher herself and her well-being. We wish her well.

"We are thankful that she was prepared to come and talk at the festival, and sorry that her health caught up with her."

Mr Holland added, however, that the absence of Baroness Thatcher would not detract too much from the quality of the festival.