The carrier has agreed a firm purchase of 100 Boeing 787s, with an option for 100 more, which it claims is the largest-ever order for long-haul aircraft by any US airline.

Deliveries will begin from 2024 and many will be used to replace Boeing 767s which operate the bulk of the airline’s Newark flights from Heathrow. All of these will be gone by 2030.

Older Boeing 777s, which also operate United’s London flights, will be replaced by 787s. As well as benefits to passengers, a carbon reduction of “up to” 25% per seat is expected.

"This order solves our current widebody replacement needs in a more fuel-efficient and cost-efficient way, while also giving our customers a best-in-class experience," said Gerry Laderman, United’s chief financial officer. 

Laderman continued: "And if the future of long-haul flying is as bright as we think it will be, United is able to capitalize on those opportunities by exercising these new widebody options – I look forward to the incremental margin and earnings these aircraft will generate."

Earlier this year, United began the largest transatlantic expansion in its history with the launch of 10 new routes, many of them unique among North American carriers. They included Amman, Tenerife and Palma. The 787 order will allow United to explore more destinations like these.

Any UK expansion will likely be triggered by a previously announced order for 50 Airbus A321XLRs. These single aisle types, due to arrive from 2024, are suited to regional transatlantic services.