Anthrax panic is threatening to paralyse America with 2,300 scares reported yesterday.

After the FBI discovered that the powder sent to the leader of the Senate and NBC in New York was a particularly virulent form of the disease, politicians were coming under pressure to conclude their legislative business and leave for their constituencies.

Britain has also had to deal with an increasing number of alerts. Government offices in Smith Square, a sorting office in Liverpool and the London stock exchange were all evacuated during on Tuesday, and the Millbank building that houses the BBC and Sky studios in Westminster was surrounded by the police last night following the discovery of a suspicious substance in reception.

Health secretary Alan Milburn yesterday urged the public to remain calm, saying it would be difficult to deliver enough anthrax to harm a large number of people.