Last June, more than 20 ships on the Black Sea noticed something unusual about their satellite-based navigation systems. Instead of their true positions well away from Russia’s south-west border, each ship’s GPS placed it inland at Gelendzhik Airport, a small terminal that serves the picturesque coastal town.

It made no sense. The Global Positioning System (GPS), the network of satellites that we rely on every day, is rarely wrong. When it is, the margin of error is only a few metres. The ships on the Black Sea were 20 miles from Gelendzhik.

There seemed to be only one explanation, although it was not one anybody wanted to countenance: GPS, the navigation and timing system on which the world runs, was being manipulated on a previously-unimagined scale.

There were no prizes as to who the chief suspect was. A few months later, Norwegian planes flying over eastern Finnmark, a county on the Russian border, lost their GPS reception for a week.

Modern life runs on GPS. Satellite navigation systems have rendered the art of map-reading practically obsolete. Multi-billion dollar apps such as Uber rely entirely on it, and farmers use it to plough their fields with millimetre precision. Less visibly but just as crucially, GPS is the clock by which the world keeps time.