Ms Loyola de Palacio has quickly established herself as the air travellers' champion since she became European Commissioner for Transport last year. An array of initiatives on their behalf by the former Spanish agriculture minister has won universal respect, although not always admiration.

As Mr Claude Probst, one of the EC's senior aviation officials, puts it, the passenger protection proposals "are not well accepted by certain segments of the industry".

Those airlines are going to be even less happy when they learn of Ms de Palacio's latest idea: to stop carriers bumping passengers off flights. Business travellers too may feel that her plans may hinder rather than help.

Ms de Palacio intends to add to other proposals restrictions on the ability of carriers to overbook flights.

The commission has already moved to improve the statutory compensation paid to bumped passengers but this, Ms de Palacio has decided, is not enough: "If you are going to a wedding and cannot get on your flight, you can claim some money but that does not give you back what you have missed. So it is not a question of raising the compensation but changing the situation."

Her own head of cabinet, she reveals, has been bumped twice in the past six months.

The commissioner, one of the commission's two vice-presidents, and whose remit also includes the politically sensitive energy brief, is considering two options and hopes to slip one of them in with the other proposals shortly to be examined by European transport ministers. The first option is to establish a distinction between a declared intention to fly and a reservation that is fully confirmed and paid for.

An intention to fly would allow the passenger to cancel their booking or the airline to give away their seat without penalty.

Once the seat is paid for and confirmed, however, the passenger would not receive reimbursement and the airline would have to allocate them a seat on the flight.

Ms de Palacio's alternative idea is merely to limit airlines' ability to overbook. This would be combined with efforts to encourage airlines to stage auctions, as is common in the US, where the carrier improves its compensation offer until someone is tempted to surrender their seat.

Airlines overbook because many passengers, especially business travellers with flexible, fully refundable tickets, fail to turn up for their flight. In one recent example, a Lufthansa flight from Frankfurt to New York on a 389-seat aircraft was overbooked by 77 seats five days before departure, but took off with 16 seats empty.

"Airlines say overbooking is in the interest of users because it gives greater flexibility in making reservations and lower prices," says Ms de Palacio.

"That is true but this is a problem that is unacceptable."

She prefers the first option because she believes it would encourage both airlines and passengers to act more responsibly.

However, Mr Don Lunn, chairman of the UK's Guild of Business Travel Agents, which met air transport officials in Brussels last week, thinks the proposals on overbooking will suit no one. "This beggars belief," he says. "Business travellers need flexibility, which is why they pay business fares. "The airlines have yield-management systems that can anticipate that and it is a pretty exact science. All this will do is drive up fares."

Ms de Palacio's new ideas on overbooking would join a wide range of measures outlined earlier this year in the EC's air passenger rights consultation. The commission is pressing European airlines to devise a voluntary code of conduct by next April. The code includes commitments on issues such as minimum levels of care for delayed passengers and offering the lowest fares available on the airline's reservations system.

However, on matters such as overbooking, Ms de Palacio feels it necessary to regulate and the proposed legislation will be finalised by the beginning of next year. Other regulatory issues will include forcing airlines to be transparent about code-sharing arrangements and clarification and standardisation of airline contracts.

Airlines claim they can put their own house in order and are particularly aggrieved about one section of the legislation that will make them compensate passengers in the event of a delay. Ms de Palacio has not yet decided how significant this compensation should be nor how long the delay before payments start. All she can say is that it will not be as little as one hour but is intended to deal with "very long delays", a phrase yet to be quantified.

Airlines counter by saying that most delays are beyond their control being usually the fault of air traffic control, the airport or simply the weather.

Ms de Palacio responds that she is working on finding a way for airlines to seek compensation from the parties that cause the original problem. But, she adds, "in the end, it is the airline with whom the passenger has made a contract, so it is the airline's responsibility".

The commissioner is also tackling the issue from the other end. It is for her efforts to create a single European airspace that she has won most praise. At present, each country controls its own airspace. The resulting lack of co-ordination among air traffic control systems, combined with the appropriation of large chunks of airspace by the military, is blamed for many of the delays faced by passengers.

Given the mass of national and other vested interests (French air traffic controllers to name but one), few leaders have plucked up the courage to confront the problem before.

Many expect Ms de Palacio to fail, despite her reputation for unblocking impasses. But she remains optimistic. "`I always trust reason and when you have a reasonable project, you are capable of succeeding," she says. "I know we are facing some questions relating to sovereignty but we do not have such difficulties regarding sovereignty in the stratosphere, which is used by satellites."

Based on this principle, Ms de Palacio is starting at the top and working down. She is aiming for a staged introduction of common airspace, beginning at 29,000 ft to 31,000 ft, where military activity is less common.

Ms de Palacio is a frequent flyer herself, about four times a week on average. "You could say I have a personal interest," she says. She also feels passengers have been overlooked by bureaucrats who have concentrated on big aviation industry issues such as alliances and landing rights.

The new proposals aim to restore the balance of power between the airline and passenger but there are undoubtedly battles ahead.