The Met Office escalated a heavy snow weather warning for south-west England and south Wales to red - its highest level - meaning "widespread damage, travel and power disruption and risk to life is likely" from 3pm.
Snow storms shut most of Ireland on Friday and forced Britain to call in the army to battle some of the worst weather seen in almost 30 years.
Around 1,000 vehicles were at a standstill, tailing back eight miles in both directions, Police Scotland said.
More than a foot of snow was dumped in some parts of the country - peaking with 34cm of snow in Wittering, Cambridgeshire.
Britain's Met Office warned that freezing rain was likely across southern England as Storm Emma pushes northwards from Portugal and France.
Temperatures dipped as low as minus 10.3C in Kinloss, Scotland, overnight.
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In response to the impending heavy snow showers all schools, community centres and libraries in Edinburgh will be closed, the city's local authority said.
Ireland was bracing for the biggest snow fall since 1982 with public transport halted and schools across the republic closed.
Stein Connelly, of Transport Scotland, told BBC Radio Scotland: "We're seeing significant weather disruption on the network, we've got all our gritters out and ploughs working right throughout the day, right throughout the night, but we're still seeing significant challenges".
LIVE: Buses delayed and suspended again in Sheffield due to snowThe updated Yellow warning states: "Patchy freezing rain will affect some southern parts of England and well as west Wales until early afternoon, leading to icy stretches which may be hard to see". Some roads may become blocked by deep snow, stranding vehicles and passengers.
Many forces warned motorists against driving unless absolutely essential, with Lincolnshire police saying travel on "most roads" was impossible.
As well as an amber warning in place until 8am this morning across south Wales, SW and south central England - there is an amber warning for snow for northern England, eastern Scotland and Northern Ireland - as further snow showers blow in off the sea here through the day - adding to already significant accumulations in places.
The chief forecaster said a weather system is expected to move slowly north through Thursday, initially affecting the south of the warning area before intensifying and pushing north across the rest of the area later on.