AIRLINES could install “spy in the cabin” systems on their aircraft in a £29m programme developed by the European Union to prevent terrorist attacks.

The EU is keen to pursue a project for in-flight monitoring of passengers with tiny cameras and microphones in aircraft cabins. Computers would constantly analyse facial expressions and conversations for suspicious behaviour, triggering alarms if certain traits were identified.

The EU has already funded a programme to develop the technology in conjunction with BAE Systems, the French company Thales, Reading University and other organisations. Fearing that airlines may be reluctant to accept or pay for such security systems, it is now holding talks about legislation.

Daniel Gaultier, one of the project managers, said: “The airlines won’t like it as it will cost. They won’t buy it unless there is legislation.”

A European Commission spokesman confirmed that talks had begun with the European parliament to plan legislation “in order for these [security] measures to be applied across [all] airlines”.

The move is provoking concerns about civil liberties. Baroness Ludford, a Liberal Democrat MEP, said: “This is an intrusive step too far. It’s not fantastic to say you might end up ‘rendered’ and taken to a foreign prison and tortured.”

As part of an EU programme called Security of Aircraft in the Future European Environment (SAFEE), researchers at Reading University have helped to develop monitoring systems that use minute cameras and microphones installed in each passenger’s seat or in overhead air vents, as well as wide-angle cameras covering the aisles.

Advanced computer software sifts the information and compares it against known risk factors. “For example, it looks for running in the cabin, standing near the cockpit for long periods and other factors that suggest a developing threat,” said James Ferryman, one of the researchers. “We have done a whole range of research on what is normal behaviour and what actions would be unusual.”

For security reasons the researchers will not reveal the telltale signs they have identified. However, they claim the system can distinguish between ordinary nervous flyers and terrorists preparing to attack.

Simple sweating or similar signs of anxiety, or indeed an argument between travelling companions, would not set off an alert. “The system will not be triggered by nervous flyers,” Ferryman said. “It is only triggered by well-specified combinations.”

Those combinations have been identified by intelligence experts and security analysts who have studied suicide bombers. Ferryman also claimed that it was impossible to fool the system by disguising behaviour.

In-flight surveillance is just one part of a drive to combat terrorists who manage to evade airport security checks. The SAFEE programme also envisages controlling access to aircraft flight decks with biometric scanners that would check finger-prints or eye patterns. Another scheme would use computerised flight systems to steer a plane automatically onto a safe path if a suicide attacker tried to fly it into a tall building.

In addition, authorities are working on a pan-European system for passing real-time information about “renegade” air incidents between Nato, national police forces, airports, airlines and other bodies.

Airlines remain unconvinced that intrusive in-flight surveillance is the best way to counter terrorist threats. A spokesman for British Airways said: “While we always welcome new research and development that advances aviation security, we believe the emphasis of any new security initiatives would be better placed on preventing potential terrorists from boarding aircraft in the first place.”

Ferryman admitted the system needed detailed testing but said it could be operational within “several years”. He said that concerns over privacy had been considered and that surveillance data would be erased after flights landed safely.

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