The “behaviour detection squads” will patrol terminals to monitor the gestures, conversations and facial expressions of passengers. One of their aims will be to spot those who may be concealing fear or anxiety.

People deemed to be acting suspiciously will be taken for questioning and prevented from flying if they fail to explain their actions.

UK trainers have studied the techniques in America, where behaviour detection squads are already deployed at airports.

The plan is part of an overhaul of passenger screening. Instead of solely relying on searches to uncover weapons and bombs, airport authorities are increasingly seeking to pinpoint the terrorists themselves.

In the long run, passengers flying from international hubs such as Heathrow and Gatwick could even face a lie-detector test before they board.

In America behaviour detection officers are working at a dozen airports, including Washington Dulles and Boston Logan. The programme, called Screening Passengers by Observation Technique, or Spot, is run by the US Transportation Security Administration (TSA).

“There are infinite ways to find things to use as a weapon and infinite ways to hide them,” said Kip Hawley, the director of the TSA. “But if you can identify the individual, it’s by far the better way to find the threat.”

Paul Ekman, emeritus professor of psychology at the University of California and a leading expert on facial expressions, has been helping to train the TSA’s officers.

Earlier this year three British officials attended a three-day course run by Ekman in Vancouver. “(They were from) a branch of your government that has similar responsibilities to the TSA,” he said.

“A year earlier, we had four people participate in a five-day course. So our work with the UK has been going on for some time. It isn’t practical for us to be the trainers for the UK, so we are training the trainers.”

Ekman added that a British official had told him last week that “things are going to start moving forward now”.

The Spot teams, who are in uniform and work in pairs at US airports, use a list of more than 30 unusual behaviours against which to check passengers. Some things they look for are obvious, such as a person wearing a coat on a hot day or pacing around, but there are more subtle signs.

“They are all things that people do with their posture, with their hands, with their heads, with their voice if you can hear it and with their gestures,” said Ekman.

In particular, officers are trained to recognise concealed emotion, such as fear or anxiety. These so-called “micro-facial expressions” appear on a person’s face for 1/25th of a second. “They are so fast, that unless you’ve been trained you don’t see them,” said Ekman.

If a passenger’s behaviour gives cause for concern, the Spot officers ask a few casual questions, such as the reason for travelling.

Those who arouse further suspicion are referred to other law enforcement officers for screening, and, if found to be involved in criminality, barred from flying.

The move towards passenger profiling follows the chaos endured by travellers at British airports in the wake of the alleged plot to blow up transatlantic airliners.

Although several airlines flying out of the UK, including Virgin Atlantic, employ security staff to carry out a basic form of passenger profiling, the government is thought to want a more centralised system in place.

This may lead airlines to adopt some of the practices of El Al, the Israeli carrier that pioneered profiling.

The process of checks start when a passenger books a flight, according to Isaac Yeffet, the airline’s former head of security.

Signs that trigger suspicion are buying a one-way ticket, booking at the last minute, paying in cash or buying a ticket for someone else. “I like to be waiting for someone of interest when he arrives at the airport, rather than for him to surprise me,” said Yeffet.

A spokesman for the Department for Transport said: “We have a layered approach to security at airports, but cannot comment further.”

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