Police patrols have been stepped up in London
But there is unlikely to be any specific and immediate threat to the UK because it is thought the terrorists do not have the means to utilise the weapons, minister Ben Bradshaw said.
Mr Bradshaw told the Australian Broadcasting Corporation: "We know that the al Qaida network has been trying to get hold of biological and chemical weapons for the last 10 years.
"We believe they've probably got some.
"What we're not sure about is whether they've got a delivery mechanism," he added.
High security alert
UK Home Secretary David Blunkett has said measures are being taken to protect vital water, electricity and gas supplies, in the wake of the first strikes on Afghanistan.
He refused to detail the action taken for fear of causing public panic.
London has been on a high state of alert since the US atrocities on 11 September, with 1,500 extra police officers on the streets.
London Mayor Ken Livingstone said a car bomb or pipe bomb were more likely threats in London than a New York-style attack, because of better security around European airports.
Vigilance plea
Foreign Secretary Jack Straw said there was still no "specific information about any specific threats" to the UK.
He warned people to be vigilant but be calm and to go about normal business.
Special efforts have also been made to prevent attacks against Muslims.
Mr Blunkett said that vigilance was primarily needed from security and emergency services, rather than the general public.
Mr Livingstone supports Mr Blunkett's plea for business as usual.
Surveillance
A Metropolitan Police spokesman said they had been vigorously planning for a range of threats on London.
Scotland Yard Commissioner Sir John Stevens has warned that although there was no specific threat against London, the capital could be a terrorist target.
Specialist police surveillance vehicles have been deployed at a series of key sites in London and the south east as part of the anti-terrorist operation.
Teams using hidden video equipment have been stationed at locations including Heathrow Airport, the Houses of Parliament and Buckingham Palace.