Heathrow was closed to incoming flights today in the wake of the anti-terror operation.

Airport operator BAA asked that all flights still on the ground should not take off for the west London airport.

National Air Traffic Services (Nats), which runs air traffic control, said that flights already heading for Heathrow would be allowed to land.

A Nats spokesman said: "BAA has asked that no flights due to come to Heathrow be dispatched."

He added that some flights were able to leave Heathrow and were being handled by Nats in the normal way.

The move came as several airlines suspended services to the UK because of the major disruption caused by tightened security measures.

It is thought that with massive queues building up at terminals all over the UK, other airports might have to suspend incoming services.

A number of foreign carriers have announced that they were suspending flights to London. These included German carrier Lufthansa, Spanish airline Iberia and Greek carrier Olympic.

British Airways said it had cancelled all its short-haul UK and European inbound and outbound flights to and from Heathrow until 3pm today.