Question of priorities | 'Epicentre' commuters | Helen Rumbelow | Ben Macintyre | Dr Mark Porter | WHO updates | Swine flu: full coverage

The world was put on the second highest possible alert of a flu pandemic last night as countries were warned that a global health emergency was imminent.

Margaret Chan, director-general of the World Health Organisation (WHO), raised the official global alert level to phase five out of six, after the new strain of Mexican swine flu was transmitted between humans in Mexico and the United States. It had spread to at least nine countries, four of them in Europe.

Dr Chan said: “Influenza viruses are notorious for their rapid mutations and unpredictable behaviour. We do not have all the answers immediately, but we will get them.”

Phase five, one step short of a full pandemic, is defined by the WHO as a strong signal that a pandemic is imminent, “and that the time to finalise . . . planned mitigation measures is short”. Phase six declares a global pandemic, or sustained community-level illness on more than one continent.

Britain is considered one of the countries best prepared for such an event. Ministers pledged yesterday to increase stockpiles of medicines, including antiviral treatments, and announced a public health campaign. The Government had indicated earlier that no big events in Britain were likely to be cancelled or borders closed as a result of the decision to raise the alert level.

The announcement came late last night after all-day emergency meetings with leading scientists, convened by the WHO. By 9pm a total of 140 cases were confirmed around the world of the viral strain of swine flu that is spreading from Mexico, including three new cases in Britain.

Up to a million doses of antiviral drugs will be delivered to frontline NHS workers by next week. Doctors and nurses will receive medication to use as a precaution if they come into contact with anyone suspected of carrying the swine flu strain.

Gordon Brown said that three new cases had been confirmed yesterday in England, including a 12-year-old girl, whose school was closed and her classmates given antiviral drugs. A 41-year-old woman from Birmingham and a 22-year-old man from London were also confirmed as having been infected. It takes the total number of confirmed cases in Britain to five, although all had recently returned from Mexico and were understood to be responding well to treatment at home, the Prime Minister said.

Keiji Fukuda, assistant directorgeneral of the WHO, said yesterday afternoon that the agency was moving closer to increasing its pandemic alert level. “It’s clear that the virus is spreading, and we don’t see any evidence that it is slowing down at this point,” he said. “Phase five is a significant milestone in terms of countries and warnings. We are dealing with sustained transmission in at least two or more countries.”

Hours later Dr Chan raised the alert level and said that the world was better prepared than ever for a pandemic. “For the first time in history we can track the infections, in real time,” she said. All countries should immediately “activate their pandemic preparedness plans”.

The Spanish Health Ministry had reported earlier that a person who had not travelled to Mexico was infected, raising fears that the H1N1 viral strain could spread between people throughout several countries if not contained.

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