Airlines were quick to offer alternative flights to travellers who were caught up in the chaos resulting from last week’s terrorism alert, but consumers say it is normally an uphill struggle to make compensation claims.

Most airlines whose flights had to be cancelled following the security alert across Britain’s airports on Thursday have pledged to offer stranded passengers refunds or new flights — even though they are not required to offer compensation when circumstances are beyond their control.

British Airways, for example, said those who could not fly last Thursday when news of the terrorist plot broke could rebook on flights leaving up to and including December 1.

Air France gave affected passengers the same deadline for rebooking, while Ryanair and BMI issued a deadline of August 24 for their customers to claim either a refund or a new flight — giving rise to concerns that some people will be unable to find suitable alternatives.

Of the other airlines, Virgin Atlantic said that passengers would be able to rebook, depending on availability, up to and including September 30, and United Airlines said that customers whose flights were cancelled would be eligible for a full refund.

Easyjet, which cancelled all its flights out of Gatwick, has yet to announce a date by which passengers whose plans were disrupted must rebook their flights.

However, figures suggest that airlines commonly deny other genuine claims for compensation.

The Air Transport Users Council (AUC) said in its annual report that complaints jumped 50% in 2005-6. It received more than 6,000 written complaints, almost three times the number the previous year, while telephone complaints from irate air travellers also increased, from 3,514 to 3,755.

Most of the complaints were about cancelled or delayed flights, although the number of people writing in about mislaid baggage also rose.

The European Union tried to make things easier for consumers last year when it introduced new regulations to stop airlines cancelling flights and abandoning passengers without offering compensation. The rules cover all flights that start or finish in the EU.

Passengers who are bumped off a flight because it is full, or prevented from boarding because it is cancelled without notice, are therefore entitled to compensation depending on the length of the flight.

People flying up to 930 miles are entitled to £178 under the new regime, while those travelling more than 2,170 miles get £420 if their flights fail to take off.

However, airlines can still wriggle out of paying up if the flights were cancelled due to circumstances outside their control. These include bad weather, mechanical faults and strikes — as well as terrorist threats.