On Thursday, the AA warned motorists to check forecasts before setting out on the road and to drive with “extreme caution”.
Devon and Cornwall Police said it had received numerous calls, external about collisions due to the conditions, and urged drivers to check the weather before travelling.
A number of train services were also cancelled in the area following the heavy snow.
The AA said it predicted a “major increase” in its workload.
Rain turned to steady snowfall over Dartmoor and Exmoor early on Thursday morning but as this turned heavier during the morning, heavy snow fell even at lower elevations.
Snow also fell for some around the New Forest and South Downs on Thursday morning.
While this area of snow, sleet and rain clears from southern England, heavy snow will continue in northern Scotland through into Friday morning.
Wintry showers will also move into north Wales and parts of north-west England later on Thursday and through the night.
Temperatures fell to -10C in Tyndrum, Scotland, on Wednesday night, but with a low of -8.7C in Topcliffe, North Yorkshire, it was England’s coldest night of the autumn so far.
It was also the coldest night of autumn in Northern Ireland with -3.9C at Katesbridge.
Temperatures will fall sharply again on Thursday night with a widespread frost and ice on untreated surfaces.