A public sector pensions strike in Britain next week could lead to “very long delays of up to 12 hours” for passengers arriving at Heathrow airport and “mass cancellations of departing aircraft”, airlines have been warned.
Delays at immigration are likely to be so long that passengers may have to be held on arriving aircraft, British airport operator BAA told airlines.
"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 all airlines which fly into Heathrow from BAA's Heathrow chief operating officer Normand Boivin.
He said that BAA had "reluctantly concluded" that the UK Border Agency would be unable to provide a contingency plan to support normal operations.
Mr Boivin said that following consultation with major carriers, it had agreed "a voluntary protocol" for all airlines to reduce inbound passenger volumes on the day of the strike next Wednesday.
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 30th to 50 per cent 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."
Mr Boivin told the 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."