A Palace spokesman said engineers took a week to flush the bug out of the water system, and the Royal Family were not affected.

He said the Queen and Duke of Edinburgh continued to live in their London residence and carry out their normal duties during the scare in mid-October.

Queen and Prince Philip did not leave despite scare

"Nobody had to flee Buckingham Palace and there were no reported cases of the disease," he added.

More than 300 staff were warned to be on the alert for symptoms of the illness, which can spread through a building's water system.

The bug was found in one section of the water supply, which was isolated so the rest of the Palace could carry on as normal, the spokesman said.

"Legionnaires' disease was discovered in the water supply on 13 October after routine tests," he said.

"It was dealt with immediately in the normal way by flushing out the system.

"Another sample was taken and 10 days' later the all-clear was given."

Elderly people affected

There are up to 200 cases of Legionnaires' disease each year with between 10 and 40 deaths in England and Wales.

More than two-thirds of cases occur in people over 50.

News of the find at the Palace comes in the same week a hospital in Kilmarnock confirmed that tests on its water supply found the bug which causes Legionnaires' disease.

A spokesman for North Ayrshire and Arran NHS Trust said the tests were carried out after an 80-year-old man died in Crosshouse Hospital, Kilmarnock, six weeks ago.

Subsequent tests at the Ayrshire hospital showed the man, from Kilwinning, had been suffering from Legionnaires' disease.