Heathrow passengers have to face longer delays on immigration clearance on Wednesday due to public sector strike. Reuters

Passengers arriving at Heathrow Airport on Nov. 30 can expect a delay of around 12 hours while longer immigration queues are cleared.

The Heathrow is heading for a "grinding halt" as immigration officers join the strike next week, reports the Telegraph.

Britain is set for a nationwide strike over public sector pension changes on Wednesday. Majority of border agency employees are expected to join the strike action along with other 2.6 million public sector staff.

"Modelling of the impacts of strike action on passenger flows at Heathrow show that there are likely to be very long delays of up to 12 hours to arriving passengers," the newspaper has quoted Normand Boivin, Heathrow's operating officer, as saying.

"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. 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," he added.

Meanwhile, BAA, the operator of the Heathrow Airport, is in talks with the UK Border Agency and the airlines to minimise the disruption. The airlines are being advised to operate with half their capacity.

A fifty to seventy percent reduction in immigration workforce is expected during the strike period and there is a possibility that those who are working would be of lesser experience in handling passport checks.

The Home office is currently trying to fill the vacuum by deploying the border agency staff who are not the union members and civil servants from Whitehall to carry out the immigration checks.

The treasury expects the strike to cost the UK economy more than £500 million and fears that it may lead to job losses.