Fred Olsen Cruise Lines has confirmed that seven passengers on a cruise out of Dover have been admitted to hospital in Sweden with pneumonia-like symptoms.

In a statement the company said the passengers, who had been on board Black Watch, were hospitalised in Stockholm on Friday. The news came amid reports that the seven, all British, were showing the symptoms of Legionnaires’ Disease.

Investigations are under way to identify the infection and where it was contracted by the passengers, who are all over 60. The ship’s jacuzzis and swimming pools have been closed until further notice as a precaution.

The condition of two passengers improved enough to allow them to return to the UK. The remaining five are reported as stable in hospital.

Black Watch left Dover on July 15 for a 17-night cruise to Lapland and St Petersburg. It is due to return to the UK today – two days ahead of schedule – with its next voyage due to begin on August 1. The ship has 756 passengers and 329 crew on board.