Heathrow Airport's runway has reopened after grounding flights following reports of a drone sighting.
Passengers had reported being stuck on the runway, with reports of police investigating possible drone activity.
The airport had earlier said in a statement on Twitter it was working with police to "prevent any threat to operational safety".
The Metropolitan Police confirmed officers were investigating the reports.
Sarah Rogers, a journalist with ITV Granada, tweeted at 5.30pm that her flight was grounded due to possible drone activity.
Transport Secretary Chris Grayling said the military were preparing to deploy equipment used at Gatwick Airport, when a suspected drone caused mayhem in December.
"We are in contact with Heathrow Airport concerning the drone sighting. I have already spoken to both the Home Secretary and Defence Secretary and the military are preparing to deploy the equipment used at Gatwick at Heathrow quickly should it prove necessary," he said.
The drone sightings at Gatwick caused days of chaos for hundreds of thousands of people in the week before Christmas.