The World Health Organisation is close to declaring a global flu pandemic after a surge in cases around the world, including the first Briton to fall critically ill solely because of the virus.
Keiji Fukuda, the official overseeing the WHO's flu strategy, said the virus had now reached 64 countries and was spreading fast outside Mexico and the US, the most heavily affected countries.
Fukuda said the organisation was now "getting closer" to declaring the outbreak had reached phase six, the highest level on their alert scale. Overnight, Chile became the latest country to declare its first swine flu death.
British health officials believe their containment strategy may no longer be working, and that the virus could be spreading uncontrolled.
Three people are critically ill in intensive care in hospitals in Scotland, including the first involving someone becoming ill wholly from the H1N1 virus.
The 45-year-old man was admitted to an isolation ward at the Royal Alexandra hospital in Paisley yesterday, along with a 38-year-old woman who has underlying health problems.
The first Briton to fall critically ill with swine flu, a 37-year-old man also with other health problems, is still in intensive care at the Victoria Infirmary in Glasgow, but is said to be stable.
To the alarm of health officials, there is no known link to the two new critical cases. They are not travel-related, nor are they known to be connected to the two other clusters in the Glasgow area.
One of those clusters surrounds the 37-year-old Sikh man critically ill in the Victoria Infirmary: three members of his family, a boy living next door and several others are now confirmed swine flu cases.
The second cluster is centred around a busload of Rangers fans from Dunoon in Argyll. Initially 13 people on the coach and seven close family members and friends were diagnosed with swine flu.
The number of confirmed cases in that cluster jumped by 14 yesterday. This morning the Scottish government announced that Toward primary school in Dunoon had been closed after a confirmed case there, while Apple Tree nursery on the Isle of Bute had also been shut. In all, 65 children will be given antiviral drugs as a precaution.
Fukuda appeared to contradict the official view in Britain that the virus was a mild one. "We do have some hesitation in calling such an infection mild," he said. "It's probably fair to call the situation something like moderate right now."
The Scottish health secretary, Nicola Sturgeon, said the emergence of the latest British cases suggested the current strategy of trying to stop the virus spreading through containment and the voluntary quarantine of suspected and confirmed cases was no longer working.
The number was likely to rise significantly in coming weeks, she added. "We're getting closer now to a situation where the containment strategy we have been pursuing up until now will evolve into something different," she said.
The new cases reported yesterday bring the UK total to 362. There are signs of a sharp acceleration in infections, six weeks after the disease first emerged in the country.
The cluster of 23 cases surrounding the Rangers supporters' bus, which came to light on Monday, more than doubled the total number of Scottish cases.
A further 23 Scottish cases emerged yesterday, with 61 confirmed cases reported by the Health Protection Agency in England – another sharp rise.
WHO officials are closely watching the outbreak in Chile. Winter is starting in the southern hemisphere, raising concerns that a winter flu pandemic is imminent. So far the virus has infected more than 18,965 people and caused more than 117 deaths.
The WHO has set aside another $500m (£302m) to help developing countries tackle the virus, while President Barack Obama's administration has asked the US Congress to set aside a further $2bn for an expected pandemic.
