A ban on carrying hand luggage on to aeroplanes could remain for some time to come, a Midlands-based security expert warned last night.

Dr David Dunn, from the University of Birmingham's school of security and diplomacy, said the threat from liquid explosives could also mean airports overhauling the checks they make on passengers.

"All luggage stored in the hold is subject to screening for explosive devices either using machines or dogs that can sniff out explosive elements," Dr Dunn said.

"That hasn't been applied to hand luggage because it was believed that metal detectors were enough to show up the detonators needed for bombs.

"That technique doesn't help us with explosive or flaming liquid substances, so it means passengers might have to put up with very strict controls or even a ban on hand luggage until it can be subjected to the same screening as other luggage."

According to experts, several different kinds of liquid explosive could have been involved in the terror plot.

Most are relatively easy to obtain or make from raw ingredients they can hidden inside innocent-looking bottles or cans.

Dr Dunn said the weapons were an example of how innovative terrorist groups, such as al Qaida, had become.

"We are dealing with an incredibly inventive and resourceful enemy," he said. "For all its horrendousness, September 11 was a clever attack. No one had imagined the use of aircraft as weapons - it was a way to use our own vulnerability against us."

Dr Dunn said since the world Trade Centre attack, there had been a number of new devices developed by terrorists to attack passenger planes.

These included the shoe bomb famously smuggled onto an American Airlines flight to Miami by London-born Richard Reid.

He added that further attacks of a similar nature were likely.

"The terrorist threat to the UK is an ongoing process," Dr Dunn said. "The Joint Terrorism Analysis Centre estimate that up to 10,000 people living in the UK could have been exposed to radical influences."

He added that although yesterday'sfoiled plot was unconnected to the crisis in Lebanon, the situation in the Middle East would only serve to aggravate the situation.

"The fact that Britain and the US have not condemned Israel's attacks has created a sense of outrage and injustice among some who believe the West is on a crusade against Islam," Dr Dunn said.

Dominic Armstrong, the head of research and intelligence at the security and risk management company Aegis, said an attack on aircraft suggested the involvement of a militant jihadist group inspired by the al Qaida leader Osama bin Laden.