Some of the biggest banks in the US and London are preparing for the possibility of a swine flu pandemic, with one acknowledging it is "dusting off playbooks" from the outbreaks of avian flu in 2003, as analysts try to predict the impact on the global markets should the virus spread.

The World Health Organisation yesterday raised its pandemic alert level from phase three to phase four, which denotes a virus that can cause "community-level outbreaks."