British Airways offers flight upgrades
One-way passengers can upgrade to the business class Club Europe cabin or to the World Traveller Plus cabin on long-haul flights.
Customers will have the opportunity to change their flight class if they check in online and may also be sent an email inviting them to upgrade before travelling.
The benefits of the Club Europe service include access to British Airways lounges at Terminal 5, while the World Traveller Plus cabin provides seats offering more leg-room than World Traveller class.
British Airways first launched its 'upgrade before you fly' option at Gatwick Airport last year.
Robert Boyle, the airline's commercial director, said: "This offer is a fabulous way for customers who might want to treat themselves to an upgrade in the last few days before their holiday.
"It has been a hit at Gatwick so we want to offer the same level of luxury from Heathrow."