Travel advice for passengers

Forty British Airways flights - mainly domestic but also including short and long-haul - were among those cancelled.

BA said about 80% of its 210 scheduled short-haul and domestic services would fly on Friday and 75% of 18 scheduled long-haul services would also operate.

Easyjet said a full schedule would resume on Friday.

Gatwick Airport said heightened security measures would remain in place on Friday and passengers should contact their airline for up-to-date travel information.

A spokesman warned people to expect delays on Friday and over the weekend, and urged passengers to prepare in advance by packing all items in their hold baggage, and allow extra travelling time to the airport.

We're responding to a very serious risk and the action is absolutely necessary Sussex Police spokesman

On Thursday, the north and south terminals were overcrowded with long queues of passengers being subjected to stringent security checks.

BAA Gatwick said passengers should check flight situations with their individual carriers, and also allow extra time to get to the airport because of long delays.

Some passengers complained of a lack of information at the airport on Thursday and tempers became frayed at check-in desks.

A spokesman for Sussex Police said: "We appreciate the action taken is causing major disruption at the airport, but we're responding to a very serious risk and the action is absolutely necessary.

"There are officers around the airport helping to attend to any problems and we hope that people are keeping calm."