Day 1 Terrorists secretly release anthrax at a packed football stadium during a match in a British city.

Day 1 Terrorists secretly release anthrax at a packed football stadium during a match in a British city.

Day 2 Everything seems normal

Day 3 Some 400 people in the city go to their GPs with flu-like symptoms. As flu has been increasing recently, the doctors suspect nothing and send their patients home with instructions to stay in bed and drink plenty of fluids.

Day 4 Some of the patients seem sicker than would be expected from a normal flu outbreak, and the firsts tests are done. They identify a bacillus bacteria, but this causes no great alert as some bacilli are relatively harmless. But patients begin dying. By the end of the day 1,200 are ill, 80 have died.

Day 5 The number of patients doubles and doctors recommend isolating victims to try to slow the spread of the disease. The football stadium is identified as the centre of the epidemic. Finally, anthrax is suspected and identified. Treatment by antibiotics is prescribed, but they have to be given early on in the infection, and there are not enough for everyone affected. Supplies of vaccines are also limited. 2,700 have fallen ill; 300 have died.

Day 6 The antibiotics run out. Media reports that they were distributed unfairly lead to riots. Doctors now realise that not all victims were at the match; some lived nearby. Study of the weather on Day 1 suggests that people living within eight miles downwind are at risk. Panic rises. Gyms and shelters are opened for the ill as hospitals run out of beds. 3,200 ill; 900 dead.

Day 7 More antibiotics arrive. The authorities announce that all the dead must be cremated. More panic. The city begins to grind to a halt as bus and train drivers refuse to enter it, even though they are assured that anthrax is not infectious. 4,000 ill; 1,600 dead.

Day 8 The city becomes virtually paralysed. Schools are closed. Medical services are running down as many doctors and nurses are falling ill. Public transport has virtually collapsed. 4,800 ill; 2,400 dead.

The number of infected people does not rise after this, as anthrax does not pass from person to person, but the death toll rises until it reaches 4,000. The area downwind from the stadium becomes known as the "Dead Zone" abandoned by families and businesses alike.

This scenario is based on one drawn up for US authorities by experts at the Johns Hopkins Center for Civilian Biodefense Studies in Baltimore. They also compiled a scenario for a release of smallpox, which would pose more difficult problems, because the disease is both contagious and has an incubation period of up to two weeks, meaning it would have spread further before being detected.