Europe's second-largest low-cost carrier after Ryanair (RYA.I) had tested the new system across 5 percent of its network during the peak season with 70 percent of passengers preferring it to easyJet's current predominantly first-come-first-serve set-up.

Faced with jet fuel prices near record highs at the same time as rising tax and airport charges, airlines are under increasing pressure to come up with ways of attracting passengers. The move also means the gap between traditional airlines and low-cost carriers will narrow even further.

In July EasJet (EZJ.L), the largest carrier at London's Gatwick airport, upgraded its profit forecast and said it had benefited from strong demand after a wet start to Britain's summer season.

The airline will announce its August traffic statistics on Thursday.

Shares in the group closed at 530 pence on Tuesday, up 60 percent on a year ago, valuing the business at around 2.1 billion pounds. (Reporting by Neil Maidment; editing by Kate Holton)

• A Permanent Economic Emergency