Economy class passengers are to be offered beds by an airline but at a price, they will have to buy three seats to qualify.

Air New Zealand said its "Skycouch" will use three economy seats that unfold to create a space where children can play or people can relax and sleep.

The deal is aimed at couples and families, and will be the price of about two and a half seats.

"For those who choose, the days of sitting in economy and yearning to lie down and sleep are gone," chief executive Rob Fyfe said. "The dream is now a reality, one that you can even share with a travelling companion - just keep your clothes on thanks."

Developed by Air New Zealand designers and engineers, Mr Fyfe said the Skycouch represented the first real improvement in comfort for economy travellers in more than 20 years and would help the airline set a new benchmark for international travel.

To create the bed, leg rests rise up to fill the space between rows of seats. A thin mattress is placed on top and full size pillows are provided. The result is a level bed across three seats, although it is not completely even due to the seat contours.

About a quarter of all long haul economy seats will convert to Skycouches, taking up the first 11 rows in the economy cabin of the airline's new Boeing 777-300 planes.

Passengers will pay the standard economy fare for two seats and receive the middle seat for about half price. Assuming a couple buys the seat, the total amounts to about £3,300 per person for a return flight to London.

Single passengers in business class lie-flat seats pay nearly £4,400 for the London flight, for example. A single premium economy seat that does not recline to a bed costs nearly £2,600.