The passenger-profiling technique involves selecting people who are behaving suspiciously, have an unusual travel pattern or, most controversially, have a certain ethnic or religious background.

The system would be much more sophisticated than simply picking out young men of Asian appearance. But it would cause outrage in the Muslim community because its members would be far more likely to be selected for extra checks.

Officials at the Department for Transport (DfT) have discussed the practicalities of introducing such a system with airport operators, including BAA. They believe that it would be more effective at identifying potential terrorists than the existing random searches.

They also say that it would greatly reduce queues at secur-ity gates, which caused lengthy delays at London airports yesterday for the fifth day running. Heathrow and Gatwick were worst affected, cancelling 69 and 27 flights respectively. BAA gave warning yesterday that the disruption would continue for the rest of the week.

Passengers are now allowed to take one small piece of hand luggage on board but security staff are still having to search 50 per cent of travellers. Airports have also been ordered to search twice as many hand luggage items as a week ago.

BAA was criticised yesterday for failing to commit itself to recruiting more security staff and for claiming that its existing 6,000 staff at seven airports would be able to handle the extra searches. Tony Douglas, the chief executive of Heathrow, said that X-ray screening of hand luggage would be much faster under the new rules on size and contents, leaving staff free to carry out more searches.

The new measures, which include a ban on taking any liquids through checkpoints, are expected to remain in place for months. A DfT source said it was difficult to see how the restrictions could be relaxed if terrorists now had the capabil-ity to make liquid bombs.

The DfT has been considering passenger profiling for a year but, until last week, the disadvantages were thought to outweigh the advantages. A senior aviation industry source said: “The DfT is ultra-sensitive about this and won’t say anything publicly because of political concerns about being accused of racial stereotyping.”

Three days before last week’s arrests, the highest-ranking Muslim police officer in Britain gave warning that profiling techniques based on physical appearance were already causing anger and mistrust among young Muslims. Tarique Ghaffur, an assistant commissioner of the Metropolitan Police, said: “We must think long and hard about the causal factors of anger and resentment.

“There is a very real danger that the counter-terrorism label is also being used by other law-enforcement agencies to the effect that there is a real risk of criminalising minority communities.”

Sir Rod Eddington, former chief executive of British Airways, criticised the random nature of security searches. He said that it was irrational to subject a 75-year-old grandmother to the same checks as a 25-year-old man who had just paid for his ticket with cash.

Philip Baum, an aviation security consultant, said that profiling should focus on ruling out people who obviously posed no risk rather than picking out Asian or Arabs.

A DfT spokesman refused to make any comment or answer any questions on profiling.

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