Picture the scene: you’re in a white-out with precipitous crags either side and you desperately need to know how far it is to the safe route off your peak.

You’re not sure just where you are on the map, so out comes your trusty GPS receiver. But there’s a problem: the signal’s going haywire and you can’t get a fix. Why? Because the satellites’ data is being jammed by the British military.

Walkers in bad weather on a summit 

From time to time, our gallant soldiers, sailors and aircrew test their ability to block the Global Positioning System by broadcasting a jamming signal which blitzes the low-powered rays from the orbiting satellites. And if you happen to be in dire need of your GPS when this happens, you’re in trouble.

So it’s as well to know when this is going to happen. Ofcom, which oversees radio communications in Britain, has a notification system to warn of upcoming blocking of GPS services to which it has been alerted.

You can sign up to be emailed about any planned loss of service at Ofcom’s website.

And in the meantime, perhaps it’s time to practise those map and compass skills – just in case.