Analysis by Spanish travel bookings group Amadeus (AMA.MC) found a 143 percent spike in arrivals on July 26 -- a Thursday and the day before the Games open -- compared with the same date in 2011, a Tuesday.

Broadened to include the four days before the Olympics, scheduled arrivals showed an increase of 31 percent. The figures were compiled from global travel agencies' air reservations in and out of London.

U.S. citizens have taken the lead in early bookings with an 82 percent year-on-year surge in reservations.

Currently, the U.S. represents 17 percent of scheduled arrivals with German travellers in second place.

During the three-week Olympics period, Amadeus data showed scheduled arrivals in Brussels were up 49 percent; Amsterdam 28 percent higher; and Paris 5 percent, suggesting travellers may be increasingly adopting high-speed rail links in conjunction with air travel to reach London.

Holger Taubmann, a senior vice president at Amadeus, said the data "could help airlines make decisions on the benefits of increasing the capacity and frequency on a given route to meet travellers' demands, or consider targeting customers with air-rail combined trip offers".

Heathrow is planning for 137,800 passengers on Aug 13. -- a 45 percent increase in departures -- making it the busiest day in the airport's history. The Games will close on August 12

In November, the European Tour Operators Association ETOA.L had said it was seeing an average 90 percent downturn in bookings during the Olympic period, estimating about 3.5 billion pounds could be lost to the British economy.

The ETOA figures added to travel-industry fears at the time that displacement -- a reduction in traditional, non-Games tourists, and an exodus of Londoners eager to escape the crowds -- would offset Olympics arrivals.

The latest figures from Amadeus also suggested Londoners do not appear to be fleeing. Its analysis of scheduled departures from all London airports found residents were 11 percent more likely to stay in the city during the Olympics period than they did in 2011.

Threats of strike action across London's public transport system by the leader of Unite, Britain's biggest union, and a dispute between the RMT union and London Underground over bonus payments, may affect travel decisions over the next few months.

The government has launched an international advertising campaign to boost tourism and plans a series of business summits during the Games it hopes will generate an additional 1 billion pounds revenue for British companies.

The Amadeus data does not take into account direct bookings to airline websites -- which accounts for 50 percent of travel bookings -- but factors in all agency reservations up to February 22.

(Additional reporting by Keith Weir; Editing by Dan Lalor)

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