HSBC warned that up to half its staff could fall ill or be absent at the height of a bird flu pandemic.

The world's third largest bank - which is based in London but has operations in 77 countries - yesterday said it was planning for a "worst case scenario" in which 50 per cent of its 253,000 employees could be off work should the deadly virus spread.

HSBC insisted it did not expect half its staff to contract bird flu and added that the figure included people absent for other reasons, including caring for family and restrictions on travel during the crisis. But the rate is higher than official forecasts, including the 25 per cent predicted by the World Health Organisation.

HSBC said: "While we have no reason to disbelieve the Who guidelines, it is entirely proper that we prepare for any contingency."

The warning came as experts battled to stop the H5N1 strain of the virus spreading after 14 cases were confirmed in Turkey.

They are the first cases in Europe and have further fuelled fears of a bird flu pandemic. It has already claimed 77 lives in six countries in the last two years.

HSBC said bird flu was a "major health threat" which it had to take "extremely seriously".

The company said: "The figure for potential staff absence of 50% does not relate to how many staff we expect to contract bird flu.

"It is a hypothetical number that we have used for worst case scenario planning and includes staff who may be unable to travel or need to take time off to care for loved ones.

"It also includes HSBC's average level of absence due to holidays, training courses, other illness and so on."

It added: "Fortunately, our scale means that we have the necessary resources to maintain a reasonable level of service even in the face of very serious threats.

"To that end, we have been planning how to change working practices to respond to a possible pandemic."

HSBC has devised plans for staff to work from home or via video link and teleconferencing equipment in the event of a pandemic. It has also been looking at office cleaning once an hour in an effort to limit infection.

It is understood that other multinational companies are making similar plans to HSBC, which has experience of dealing with serious health risks, including the Sars crisis in 2003 which affected its activities in Asia and Canada.

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