EMBARRASSED scientists were forced to withdraw a red alert that the Northern Lights would be visible across all of the UK after a lawnmower wrongly triggered sensors.

The alert was issued by experts at Aurora Watch UK after the magnetometer at the University of Lancaster recorded a surge in geomagnetic activity.

Subscribers to the AuroraWatch UK mailing list were sent a red alert informing them that it would be possible to view the aurora borealis from anywhere in the UK.

But this extraordinary alert was withdrawn just four hours later when it was discovered that a groundskeeper driving a sit-on lawnmower had disturbed the readings of a local magnetometer.

Aurora Watch UK, which is made up of members of the Space and Planetary Physics group at Lancaster University’s physics department, usually rely on readings from a magnetometer at Crooktree, near Torphins in Aberdeen, but as it had been “playing up” they switched to a backup device in Lancaster – with unexpected consequences on August 23.

The project draws on magnetometers in Lancaster, Aberdeen, the Faroe Islands and further afield.

Aurora Watch UK is run by scientists at the university and takes readings from lots of magnetometers to work out when the aurora borealis will be visible across Britain.

It said it was looking into ways to prevent any repeat of the confusion.

An update posted to the Aurora Watch webpage said an investigation had revealed that a groundskeeper using a “sit-on mower” to trim grass had been driving too close to the sensor, prompting the spike.

“We’ll work with the facilities team to try and avoid an incident such as this occurring in the future,” said the scientists.

They explained any metal placed on the instrument or machinery operating nearby could trick it into recording more activity than was actually present.