Departures from London’s Heathrow Airport were suspended for about an hour overnight after a drone sighting.

The shut down comes just three weeks after Gatwick, Britain’s second-busiest airport, was closed over three days because of drone sightings.

Heathrow Airport tweeted: "We are responding to a drone sighting at Heathrow and are working closely with the Met Police to prevent any threat to operational safety. As a precautionary measure, we have stopped departures while we investigate. We apologise to passengers for any inconvenience this may cause."

About one hour later it tweeted: “We continue to work with the Met Police on reports of drones at Heathrow. We are working with Air Traffic Control and the Met Police, and have resumed departures out of Heathrow after a short suspension. We will continue to monitor this and apologise to anyone that were affected.”

More than 1000 flights and 140,000 passengers had they travel plans thrown into disarray when Gatwick was shut down before Christmas.

Last month Gatwick announced that it had spent US$5 million buying a system to prevent future incidents.

Heathrow Airport has also said it was buying systems to guard against drones.

Heathrow is the second busiest airport in the world, measured by international passenger traffic, and the seventh busiest in the world by total traffic.

The airport handles 1300 flights a day and 220,000 passengers.

Last month, one of the world’s leading experts in cybersecurity, Edith Cowan University’s security research institute director Craig Valli, said that there’s a sinister side to drones.

“These ‘toys’ can be used as weapons of mass destruction and you could, for instance, launch 50 to attack an airport. And that attack could be pre-programmed.”

The capability of drones, which can deliver explosives or bacterial contaminants and cost as little as $300, was growing rapidly with lighter, more powerful batteries and more sophisticated software, Professor Valli said.

“What you buy today, in nine months you will have twice the capability,” he said.

An Australian company, which claims to have the technology which could have prevented Gatwick’s travel chaos, has warned airports will increasingly need anti-drone defences as remotely piloted aircraft become more sophisticated.

Sydney-based Droneshield has been working on technology for the last five years to detect unwelcome drones and bring them down.

The technology has attracted the attention of police and military forces. Droneshield chief executive Oleg Vornik said the technology was “highly applicable” to airports such as Gatwick.

Mr Voernik said the company’s technology would have detected the drone, brought it down and helped authorities track down the operator.