The swine flu outbreak could become as severe as the flu pandemic that swept the world in forty years ago and caused more than a million deaths, according to the public health expert leading Britain's fight against the virus.
Dr Maria Zambon, head of the National Influenza Laboratory at the Health Protection Agency's Centre for Infections, said epidemiologists were conducting detailed modelling of how the new H1N1 virus will spread around Britain.
She said that while it was still too early to give an accurate picture of the severity of the disease and how many people it may infect, the early indications are that it is unlikely to cause a serious pandemic like the Spanish influenza pandemic of 1918 that claimed 40-50 million lives.
Current estimates suggest that if the Mexican swine flu virus does spark a pandemic, it will follow a similar pattern to the Hong Kong flu pandemic in 1968, which caused 30,000 deaths in England and Wales.
She said: "The modelling work to understand how these outbreaks may develop in the UK are still under way.
"Our guess at this stage, however, is that it could be as serious as the 1957 or 1968 pandemics. It is highly unlikely to be as severe as the 1918 pandemic.
"But it is worth remembering that influenza is an unpredictable virus. The virus we have here is an animal virus that is not adapted to human beings, but it is very likely it will adapt to humans."
The 1968 Hong Kong flu pandemic was cased by the H3N2 strain of the virus, which spread through out Asia before moving to Australia and Europe. It is probably the mildest of the three pandemics that occurred during the 20th century.
The Asian flu pandemic in 1957 caused an estimated two million deaths worldwide.
Advances in antiviral drug development and vaccine technology, however, since then are expected to help control the spread of the virus and limit the number of deaths.
Experts at the National Influenza Laboratory have been working around the clock since reports of the new virus began to emerge from Mexico and the United States a week ago.
An Emergency Operating Centre has been set up at the Centre for Infections in Colindale, north London, where epidemiologists and virologists are monitoring the spread of the virus in the UK.
Flat screen televisions beam in the latest news reports from around the world while dedicated phone lines allow regional health authorities to report cases as they happen.
In the laboratories, scientists have analysed more than 800 samples from patients who have presented around the country with flu-like illnesses over the past week.
They are also working to develop faster diagnostic tests that will be sent out to local health authorities and hospitals to speed up the diagnosis of swine flu in potential patients.
Epidemiologists are also studying the virus in an attempt to identify the groups who may be most vulnerable and need to be vaccinated first.
Sophisticated computer models are also being used to simulate the virus's spread around the country over the coming months and how long it may last.