HSBC, the world's third largest bank, is estimating that up to half of its staff could fall ill or be absent from work at the peak of the next flu pandemic, as Europe began to come to terms with the first human cases of the H5N1 bird flu virus on its doorstep.

The 50 per cent figure is double the rate forecast in draft guidelines for businesses being drawn up by the World Health Organisation. They will advise planning for 25 per cent absence, and the HSBC estimate is the most explicit warning yet that governments may be underestimating possible disruption.