Princess Margaret may have suffered a second stroke, Buckingham Palace said last night.

After carrying out medical tests, doctors believe the Queen's sister may have had a further minor stroke, or is still suffering the follow-on effects of her mild stroke, almost three years ago.

The 70-year-old Princess has been largely bedridden at Sandringham, the Royal Norfolk estate, over Christmas and much of the New Year.

Last night, Buckingham Palace issued the following statement:

"Evaluation of a range of test results by Princess Margaret's doctors, conducted against the background of her previous stroke in February 1998, has suggested that Princess Margaret may recently have had a further minor stroke, or be suffering from the follow-on effects of the earlier event.

"It will be some while before the success of the present treatment can be judged and the extent of her recovery can be determined, with a view to her deciding on what kind of public engagements she will wish to fulfil in the future.

"Princess Margaret's health obviously remains a matter of concern to the Queen and other members of the Royal Family.

"But the situation is stable and Her Royal Highness will be remaining at Sandringham House where nursing care is available."

Doctors say the Princess's condition is not life-threatening.

Her children, Viscount Linley and Lady Sarah Chatto, have now left Sandringham, after the Christmas and New Year period, and are keeping in touch with their mother by telephone.

Although Margaret is spending most of her time in bed, she has been able to walk since New Year's Day.

A doctor was first summoned to Sandringham on Saturday and called again on New Year's Eve, amid media speculation that the Princess was suffering from acute depression.

Friends insisted, however, that the problem would be diagnosed as physical and not psychological.

The Royal doctor called at Sandringham again yesterday before the Queen authorised the Palace statement.

But doctors hope the tests have pinpointed the Princess's illness, which was initially confused with tiredness.

On Christmas Day, the Palace said the Princess was "too tired" to attend church with other senior Royals, including the 100-year-old Queen Mother who is recovering from a broken collar bone but managed an appearance.

Margaret has been seen on relatively few occasions recently following a series of health scares