An image from Hong Kong's Mass Transit System

Malcolm Rees, a lecturer in health economics from the University of Buckingham, said that the SARS illness, which has so far killed almost 80 people worldwide, is likely to turn into a global epidemic.

In these circumstances, he told the BBC, millions would die.

UK health ministers insist that there is a high degree of vigilance among doctors looking for signs of an outbreak.

Mr Rees, who has studied the rise of the Aids virus: "It does look as if this one is really serious.

"It's got into 22 countries so far and case numbers are rising rapidly as well."

He said that the UK health authorities should prepare to treat patients at home rather than hospital in order to limit the spread of the infection.

So far the effect of SARS on the UK has been limited to just three probable cases, none of which has proved fatal.

Two more suspected cases emerged in Scotland on Thursday.

Mr Rees' intervention comes just a day after one of the world's leading infectious disease experts warned of the possibility of a global pandemic of SARS.

'Too late'

Dr Julie Gerberding wrote in the New England Journal of Medicine that it was possible that the scientific effort would not be enough to stem the rise in cases.

The World Health Organisation has told travellers to postpone non-essential trips to Hong Kong and China's Guangdong province - thought to be the epicentre of the outbreak.

A team of inspectors from the WHO is currently in Guangdong looking for the source of the infection.

There have been thousands of probable cases of Severe Acute Respiratory Syndrome (SARS) and almost 80 deaths from the virus worldwide.

The stakes are high, and the outcome cannot be predicted Dr Julie Gerberding, CDC

US Deputy Secretary of State Richard Armitage said all family members and non-essential diplomats would be offered free flights out of China.

The same offer has already been made to staff in Hong Kong.

Significant risk

Three people so far have been admitted to hospital with suspected Sars cases.

Two have now been discharged - but one is still in hospital in London.

Sars outbreaks China 1190 cases (46 deaths) Hong Kong 734 (17) Singapore 98(4) Vietnam 59 (4) Canada 62 (6) Thailand 7 (2)

Sir Liam told the BBC: "It's clear that the disease hasn't come under control in Hong Kong and Guangdong province.

"We're not looking at a global problem on the scale of the influenza epidemic which happened at the turn of the last century, but it is a pretty serious form of pneumonia."

Seventy nine people are now reported to have died worldwide.

Around 2,270 people have been infected worldwide, causing widespread fear and the imposition of emergency measures.

Death rates

The WHO estimates Sars will prove fatal in around 4% of cases, usually where the person has an underlying condition such as diabetes or a weakened immune system.

But it said that in 90% of cases, people seem to recover around a week after being infected.

How Severe Acute Respiratory Syndrome has spread around the world SARS guide

Scientists are worried about Sars because it is possible that it could, in some cases, become airborne and infect people far more easily.

If this is the case, then it would become far more difficult to contain.

There is now strong evidence that the illness is caused by a new strain of Corona virus, although this is not yet proven.

The WHO delegation in Guangdong province will investigate theories that the virus "jumped" from animals into humans.

The WHO travel advice does not apply yet to other areas, such as Singapore, Vietnam or Canada, where outbreaks appear to have been effectively contained.

As well as the latest deaths in Guangdong, China said there were 361 new cases in the province in March.

Health officials said several cases of Sars have also been discovered in Shanghai, China's second-largest city.

In Taiwan, a 30-minute public information programme about the risks of Sars was broadcast on Thursday.

Teachers, government employees and servicemen were all "obliged" to watch it.