Warning: the 20-year-old Global Positioning System (GPS) that makes your car satnav work could soon fail. GPS devices calculate your position using signals from four different orbiting satellites, and a minimum of 24 satellites is required to keep the network running. There are currently 31 in operation, but several are well past their life expectancy and a US Air Force programme to replace them is way behind schedule. This time next year, we might have to revert to old-fashioned maps to find our way - only some younger drivers will have no experience of this ancient method of navigation. So how do maps work? Space does not permit full written instructions, but here are some Frequently Asked Questions to get you started:

How do I turn it on? An atlas operates much like a book, while a map unfolds, accordion-style, to form a large sheet. This should be held in front of you so that any writing is right side up.

Now I can't see anything! Stop driving. Never attempt to operate a map and a motor vehicle at the same time.

I need to get to Redditch. What do I press? Locate "Redditch" on your map and press it with one finger. Find your current location and press it with your other finger. Now find an unbroken line that connects the two fingers. That is your "route". You are ready to begin your journey.

I've been driving for 40 minutes and it still hasn't said anything. Should I just keep going straight? The map will not issue instructions. It is up to you to compare the route on the map with information gleaned from your surroundings, and drive accordingly.

Sorry? For example - what does the sign you are passing now say?

"Croeso i Gymru." Is that good? You're on the Welsh border. Try to find yourself on the map.

I'm right near the edge of the paper! Is it trying to tell me to drive off a cliff?Don't be silly. If your satnav told you to drive off a cliff, would you?

I've got quite a funny story about that, actually. Oh, pull over and ask someone.

OK. How do I turn this thing off? It's a map. Just fold it up the same way you unfolded it, only backwards. Any other questions?

Yes. How do I make it sound like Joanna Lumley? Let's save that one for next time.