As gritting trucks work around the clock during the first cold snap of the year, spare a thought for the miners who dig the salt out of the ground almost a mile down under the North Sea in temperatures which can hit 40C.

As temperatures have dropped and icy weather has hit the UK, you've probably run in to some gritter salt on our roads. If you've ever stopped to take a look at a gritter, you may find yourself wondering where exactly all the salt comes from.