Complaints about delayed flights, overbooking and lost luggage nearly trebled last year after new European Union rules forced airlines to give passengers information about their rights, including compensation.

The Air Transport Users' Council (AUC), the airline passengers' watchdog, said the number of written complaints it received rose to just over 6,000.

It had expected a rise in complaints after the new rules but said airlines still needed to improve their customer service.

"The increase should not be interpreted as indicating three-fold increases in incidents of denied boarding, cancellations or delays," the AUC said in its annual report.

"It is more likely a function of passengers seeking to assert their newly acquired rights, and of the requirements that airlines give passengers... details both of their rights and of the organization to which they can complain."

The AUC's head Tina Tietjen said that while airlines have worked hard to adapt to the new regulations, many needed to do more.

"There remain too many occasions when those suffering delays and cancellations are often not getting their full entitlement."

In February 2005 passengers were given new rights to compensation -- based on a sliding scale -- for delayed or cancelled flights.

The longer the delay and the greater the distance of a cancelled flight, the higher the compensation levels. The EU rules were also designed to stop airlines from deliberately overbooking flights which leads to passengers being "bumped" onto later departures.