The airline will then board middle seat passengers, followed by aisle passengers, under the new policy, which will be introduced from next week.

It comes after the US airline tested the scheme - known as "Wilma" for window, middle, aisle - at four domestic locations and one of its hub airports.

The policy saved up to two minutes of boarding time per flight during the trial, according to the airline.

United said customers on the same economy reservation, such as families with young children, will still be able to board together under the new policy.

The airline will also keep its current boarding policies for travellers with disabilities, unaccompanied children, and those on active military duty.

Customers in first class and business class will see no change in their boarding process.

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The policy will be implemented on US domestic flights and some international flights - though it is not yet clear which ones.

United Airlines - the third largest airline in the world in terms of fleet size and number of routes - operates eight hub airports in the US and flies to 800 destinations worldwide.

The company also offers flights from the UK to over 340 destinations.

The airline said in an internal memo that it will implement its new boarding scheme on 26 October.