False alarms are psychologically damaging, say experts
Hundreds of workers were evacuated after a suspect letter addressed to Prime Minister Tony Blair was found - the latest in a series of bio-terror scares across the UK.
Home Secretary David Blunkett is looking at increasing the maximum penalty for hoaxers from six months to seven years - putting them on the same level as bomb hoaxers - to prevent further disruption.
Britain's emergency services have been issued with new guidelines on how to cope with an anthrax attack, but the public has been urged to stay calm.
'Malicious acts'
Fifteen workers who came into contact with the suspect envelope in Birmingham were sent to hospital for checks and have been given the all clear.
Tests have shown the letter was harmless and staff were allowed to return to work on Thursday morning.
As the anthrax scare gripping America continued to cause disruption in Britain, Mr Blunkett said: "Hoaxes cause considerable upset and disruption as well as wasting the valuable time of police and emergency services time.
"These are malicious and criminal acts and anyone sending hoax packages or misleading the police will be prosecuted and may face imprisonment."
Updated advice
Britain's emergency services have been issued with new guidelines on how to cope with threats from conventional, nuclear, biological or chemical weapons.
Updated guidance to health professionals includes advice on botulism, plague, small pox, as well as anthrax.
But the UK's chief medical officer Professor Liam Donaldson said there was not thought to be "any real threat" to the population.
Urging the public to remain vigilant, he added: "Anthrax is not a particularly good biological weapon but a hugely successful psychological weapon."
Series of alarms
There were a further series of false alarms on Wednesday, including evacuations after suspect packages were found by postal workers in Hatfield and Chelmsford.
British charity Sense - which works with people who are both deaf and blind - cancelled a fundraising mailshot to 20,000 people on Wednesday, because it contained a sachet of bath salts.
In Essex on Tuesday, the sorting of overnight mail was disrupted after a suspect package prompted the evacuation of a sorting office near Chelmsford.
There were also alerts at postal sorting offices in Preston and Bradford, on Tuesday.
Other locations hit by false alarms include the Bush House, in London, the London Stock Exchange, Canterbury Cathedral and the Driver and Vehicle Licensing Agency headquarters in Swansea.