AIRPORTS around Europe were on high alert last night after the British government warned of a possible al- Qa'ida attack.
The British Department of Transport has sent a letter to the air transport sector, saying: "There are indications that al-Qa'ida may be considering an attack against an airport or aviation sector target.
"The economic, political and psychological significance of the aviation sector coupled with the large crowds present within some of its major assets would enable a successful attack to fulfil al-Qa'ida's objectives."
Counter-terrorism advice to the transport sector had updated the threat to "severe", meaning an attack was considered highly likely, a British security source said, although there was no intelligence of any imminent assault.
Britain's national threat level has been at severe for a year and officials played down the significance of the change for airports and railway terminals, indicating it was a precautionary measure. The letter emphasised that no changes to security measures had been made as a result and that the planned method of attack was unclear.
An American intelligence official said US authorities were aware Britain had raised its threat alert level for transport hubs but added there was little indication of any increased threat to the US.
The official said last night that British authorities had taken the action based on recent intelligence reporting which suggested increased threats against transport targets, but was vague regarding the timing or tactics of any possible attack.
A senior Iraqi official said last month that he believed al-Qa'ida was planning attacks in the United States, Britain and Europe around Christmas, one year after a failed attempt to bomb a US-bound airliner.
"The government has made no secret of the fact there's an ongoing threat of a Mumbai-style attack by al-Qa'ida which has been threatened across Europe," a British government source said.
"Terrorists are forever talking about their aspirations to attack targets of significance in the Mumbai-style scenario that involves any crowded place, which is what airports and railway terminals are."
British police and security services have investigated dozens of suspected plots and arrested hundreds of suspects since the September 11, 2001, attacks on the United States.
Fifty-two people were killed in London in 2005 when four British Islamists blew themselves up on underground trains and a bus, and the last attempted attack occurred in 2007.