Truth: Decontaminating after an anthrax scare...

Thus Smallpox 2002: Silent Weapon, a docu-drama about a fictional bioterror attack made by Wall to Wall for BBC Current Affairs, has taken on a grim resonance.

In researching the film, its makers discovered how low the UK's vaccine stocks are compared with the United States.

As bioterror panic gripped the world after the 11 September attacks, the US Government stepped up its order of smallpox vaccines so as to have a dose for every American.

...and fiction: Emergency workers on smallpox alert

Yet in the UK stocks are at about the same level as in 1994, when the government reported to the World Health Organisation that it held 3.65m doses - enough for just over a fifth of the population.

That figure was based on 25 doses in each of the 146,000 vials thought to be held. At best, these vials could yield up to 100 doses each, providing almost 15m doses.

Although the Health Secretary Alan Milburn has signed an agreement with the Americans and others to share vaccines in an emergency, the UK has not brought in further supplies.

No immunity

Smallpox kills a third of those it infects. There is no cure and nearly everyone is susceptible.

Deadly disease

300m people died from smallpox in the 20th Century alone

Vaccination stopped when the disease was declared eradicated in 1980, and just one in five of those inoculated before this retain any immunity.

As a direct result of its eradication - after which the virus was kept in just two laboratories, one in the US and one in Russia - smallpox has re-emerged as a potential threat.

In 1992 a Soviet defector, Dr Ken Alibek, revealed to American officials that he had overseen an illegal programme to develop the disease into an effective biological weapon.

In the film smallpox spreads from New York to London and beyond

Since the break-up of the Soviet Union, many of its bioweapons specialists are believed to have continued their work in other countries.

The film is made in collaboration with bioweapons experts, public health officials and survivors of the last major smallpox outbreak in Yugoslavia in 1972, and aims to raise awareness of the need to prepare for such an attack.

Preview writers have compared it to the seminal 1980s dramatisations of nuclear holocaust - Threads and When the Wind Blows.

'Alarmist tale'

Producer Simon Chinn says nothing seen on the news recently compares with the devastation a smallpox attack could bring.

Although the risk of such an attack is low, experts and policy makers keep coming back to the thorny question of whether we could cope with such an outbreak.

Is Smallpox 2002 alarmist or a wake-up call?

Soviet defector Ken Alibek appears as himself

Ken Alibek, the Soviet defector who alerted the Americans to the potential threat, also took part and appears as himself in the film.

Other scientists have said that the film is alarmist and exaggerates the dangers of a biological attack.

Nevertheless, recent events have given the docu-drama an immediacy the filmmakers never envisaged when they started their research two years ago.

Smallpox 2002: Silent Weapon will screen in the UK on BBC TWO at 2100GMT, Tuesday, 5 February.