Two of the pensioners, who are from Christchurch in Dorset, are in a critical condition in a hospital in Colmar in the Alsace region of France.

The third woman, Felicity Lodge, 65, from Melksham, Wiltshire, is said to be a serious condition at the same hospital.

The three women were on two separate trips but all three had stayed at the same Belgian hotel and authorities are now investigating the property as a possible source of the infection.

'Common link'

Tour operator Wallace Arnold Holidays confirmed the passengers were suffering from Legionnaire's disease.

A spokesman said: "All three passengers, from the Dorset and Wiltshire areas, are being treated at a hospital in the Alsace region of France where their conditions are described as very poorly.

"The matter is specifically being investigated by the French health authority, the body responsible for identifying the source, and we are awaiting their findings.

"There appears to be one common link to both tours - a hotel in Belgium, although since the investigation is still ongoing it would inappropriate to speculate further at this stage.

"All passengers on the two tours concerned have been made fully aware of the situation."