British Airways planes / Getty

Flight was flying from London to Seattle

A British Airways transatlantic jet has returned safely to Heathrow after declaring a mid-air emergency over the Scottish Highlands.

BA flight 49 to Seattle took off from Heathrow shortly after 2.30pm with 218 passengers and 14 crew on board. Nearly an hour into the flight, while the Boeing 777 was above Rannoch Moor, a technical problem led the pilots to turn around. It is understood that the problem related to the cabin pressurisation, and some reports suggest that the crew were using oxygen masks.

The aircraft’s transponder transmitted the international emergency code, 7700. Despite a number of possible diversionary airports such as Glasgow, Edinburgh and Manchester, the captain decided to return to Heathrow.

The plane lost altitude and circled over the Irish Sea to dump fuel before returning to the airport. It landed on the northern runway at Heathrow shortly before 5pm.

It is understood the captain declared a “Pan” - one level short of a “Mayday” - indicating a serious problem but not a life-or-death emergency.

A British Airways spokesman told The Independent: “The aircraft has landed safely. Our highly trained pilots returned to Heathrow as a precaution after a suspected technical fault. The safety of our customers and crew is always our top priority.”

As is normal for aircraft that have declared an emergency, BA49 was given priority to land. Other arriving aircraft were forced to hold, at one of the peak times for flight movements.

British Airways has prepared another aircraft and fresh crew to operate the flight later this evening. It is expected to take off at around 9pm, with passengers arriving in Seattle around seven hours behind schedule.

The aircraft type is the same as the plane that crash-landed just short of the runway at Heathrow in January 2008 at the end of a flight from Beijing. The investigation into that accident blamed ice crystals blocking the fuel supply to the engine. All Boeing 777s with Rolls-Royce engines have been modified to prevent a repeat.