JOIN USIn fact, passengers may face upto a 12-hour delay before completing immigration formalities, and some may be confined to their aircraft if the lobbies get clogged with incoming passengers in one of the busiest airports in the world.
British immigration officials posted in India and other countries have been offered free travel to London to stand in for the officers who will be on strike.
They could also spend some time with their families when they volunteer for this duty, officials said.
Heathrow chief operating officer Norman Boivin said there was a danger of "gridlock".
The strike is scheduled for 30 November, but it will be days before situation returns to normal if the strike leads to the anticipated ‘gridlock’.
A spokesman for Prime Minister David Cameron said: "At the very least there will be longer queues and people will have to wait longer at borders," and added that the government was still working on contingency plans and gathering information on the impact of the strikes.
In a letter to all airlines operating into Heathrow, Boivin said: "The delays at immigration are likely to be so long that passengers could not be safely accommodated within the terminals and would need to be held on arriving aircraft".
He added: "This in turn would quickly create gridlock at the airport with no available aircraft parking stands, mass cancellations or departing aircraft and diversions outside the UK for arriving aircraft.