Nato has imposed an air exclusion zone over Serbia, Macedonia, Albania, and Bosnia, and there is restricted flying over Croatia and Hungary. Airlines have been forced to cancel or re-route flights, adding to journey times and fuel costs. It is understood 30 per cent of flights in Europe are being delayed because of the military operations.
Kieran Daly, editor of Air Transport Intelligence, an internet wire service, said this would put Europe's air traffic control system under huge pressure. "It will add to what is already very severe congestion in European airspace," he said. "We have reached the point where the airspace is full.
"When whole chunks of airspace are no-go areas, it starts to become horrific because of the knock-on effects. The whole system is hit by a ripple effect. But for obvious reasons the airlines are not making a noise about it."
The Guild of Business Travel Agents said people were putting off business trips because of the war. "The majority of business travellers are not going to that whole region," said the guild's chairman, Don Lunn. "It is even affecting southern Italy."
Southern Mediterranean holiday resorts are braced for a surge in bookings as holidaymakers scrap plans to go to central Europe and the eastern Mediterranean. Ian Epps, director for emerging markets at American Express Europe, said: "Some people will feel averse to travelling to Greece, Cyprus and Turkey, and many will be looking for other destinations such as Spain, Portugal and southern Europe."
The Association of British Travel Agents (ABTA) believes tourism would be affected if the allies launched a land campaign. "I can expect people to feel negative about going away and lying in the sun while people they know might be on active service," said a spokesman, Keith Betton.
Thomson Travel Group, which owns Thomson Holidays, said the conflict - combined with threats by Turkish Kurdish guerrillasto kill tourists - could hit profits. Paul Brett, the group's chief executive, said eastern Mediterranean destinations had been weakened by the war, although demand for holidays in the western Mediterranean remained strong.
Lufthansa said the fighting contributed to a fall in profits to DM111m (pounds 37.3m) from DM324m in its latest quarter. The chairman, Jurgen Weber, said increased military air traffic at Frankfurt, the airline's hub, had added an additional 20 to 30 minutes to flying times.
According to British Airways, however, the no-fly zones have had a "minor impact". Flights to destinations such as Istanbul, Athens, and Venice were being delayed, said a spokesman, but the increase in fuel use was minimal. "We have obviously suspended flights to Belgrade," he added, "but that was not a great money-spinner."