The UK faces an 80%-90% chance of a terrorist attack before May 2005, according to a leading risk forecaster.
But Simon Sole, managing director of political risk forecasting firm Exclusive Analysis, told a seminar held by the International Underwriting Association that the chance of an attack between now and the end of summer was relatively slim.
He said: "A major attack on the UK is 10% likely this side of August, 30%-40% likely this side of Christmas and 80%-90% likely this side of May."
He said that an arson attack on a tube train, such as the attack in South Korea in 2003, was more likely than a bomb or chemical attack, as it requires relatively little equipment or planning.
Sole said it was not surprising that since 2001 there has not yet been an attack in the UK. He said that terrorists were unlikely to risk transporting a high-value weapon to the UK, and were instead more likely to use such a weapon in the country they obtain it.
Sole also described al-Qaeda as a "largely defunct organisation" and said that Osama bin Laden was most likely dead. He said that Sunni extremists, such as those responsible for the Madrid bombing, now posed the greatest threat to the UK, but that they were currently disorganised, highly factional and not well trained.
A new political and economic risk map, produced by Aon, lists the UK at the highest risk of attack by Islamic extremists, single interest groups, such as animal rights activists, and nationalist and separatist movements, such as the IRA.