A British-built spy plane has set an unofficial world record for the longest continuous unmanned flight. The aircraft, a Zephyr, stayed aloft for 82 hours and 37 minutes powered by solar panels and a rechargeable battery at night.

The flight, at the US army's Yuma ground in Arizona, more than doubled the record time but, since it was done to test the ability of Zephyr to relay ground radio messages, did not fulfil all the requirements of a world record attempt.

However the aircraft's designers, at the defence firm QinetiQ, in the UK, think the plane could fly indefinitely. "We think the aircraft, in future, will be capable of weeks or months duration," said Paul Davey, Zephyr's business development director at QinetiQ.

The Ministry of Defence has funded the £20m development of Zephyr so far. The flight - partly autonomous and partly controlled from satellite - took place from July 28-31. Davey said the challenge had been to make an exceptionally light aircraft - it weighs 30kg (66lbs) - strong enough to carry a payload of up to 2kg to about 60,000ft.

Zephyr has a carbon fibre frame and is covered in super-light solar arrays thinner than paper. Its rechargeable battery is twice as efficient as any other in the world. It is launched by three people holding it above their heads as they run.

The current official world record for an uncrewed flight stands at 30 hours 24 minutes and was set by Global Hawk in 2001.