Air passengers could face delays of up to 12 hours at London's Heathrow Airport when public sector unions stage a mass strike in Britain on Wednesday, the airport's operator warned.
Operator BAA said on Friday the strike could lead to "very long delays of up to 12 hours" for arriving passengers and "mass cancellations of departing aircraft" at Heathrow, one of the busiest airports in the world.
Passengers are likely to be delayed so long at immigration that they might have to be held on board aircraft, BAA said.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
"This in turn would quickly create gridlock at the airport with no available aircraft parking stands, mass cancellations of departing aircraft and diversions outside the UK for arriving aircraft," BAA added.
The warning came in a letter to airlines which fly into Heathrow from BAA's Heathrow chief operating officer Normand Boivin.
He said BAA had "reluctantly concluded" that the UK Border Agency would be unable to come up with a contingency plan to guarantee normal operations.
He went on: "We will plan for a normal flight schedule, but we are requesting all carriers to reduce load factors on each international flight arriving into Heathrow on November 30 to 50 percent of normal levels.
"By following this protocol, airlines will reduce the risk of being diverted to an airport outside the UK and reduce the risk of having an outbound flight cancelled."
Boivin told airlines that Heathrow would do all it could and "may also be obliged to advise arriving passengers... that they should avoid arriving into the UK on November 30 unless absolutely necessary."
Major airlines have agreed to reduce the number of passengers arriving at Heathrow on Wednesday, the letter said.
British Airways and Virgin Atlantic Airways have said the normal charges for rebooking flights will not apply for those who decide not to travel on November 30.
The Border Agency said on Thursday Britain was lining up staff from embassies abroad and civil servants to replace immigration officials at ports and airports who join the strike.
Unions say they expect up to two million people to go on strike in protest at moves by the coalition government to raise the public sector retirement age by up to six years to 66.
Some public sector employees are being asked to pay a 50-percent increase in employee contributions and others will see their final salary pensions replaced by those based on average career earnings.
