Transport Secretary Lord Adonis has told local authorities and the Highways Agency to protect salt supplies further amid forecasts of 10 more days of freezing weather.
Councils that had already agreed to cut gritting by 25% are now having to almost halve the amount of salt used.
"If we did not act decisively, reserves would run down fast and essential roads would be at risk of closure if the freeze continues," said Lord Adonis.
Many police forces are advising drivers to stay off the roads for all but essential journeys:
* Police say black ice is a major problem in North Yorkshire, where two gritting lorries slid off the road. West Yorkshire Fire Service reported a spate of incidents, including two vehicles hitting buildings
* In Sussex, where 5cm (2in) of snow fell overnight, police have had reports of 70 incidents, many weather-related, such as minor crashes and stranded cars blocking roads
* A number of roads in the Highlands were closed, while motorists were travelling in convoy behind a snow plough on the A9 between Kingussie and Blair Atholl, Perthshire
* The A470 between Merthyr Tydfil and Brecon was shut in both directions with local diversions in place
* Motorists became stuck in snow on the Hilltown to Kilkeel mountain road in County Down after ignoring Road Closed signs
* Eleven train operators - including Eurostar - report disruption, with signalling problems between Hereford and Worcester causing delays. Southern train services around Brighton are subject to delays and replacement by buses.
* Buses continue to replace East Coast trains between Edinburgh and Glasgow, and Inverness and Perth, while some services through North Yorkshire and local to Manchester are still affected.
* Snow and ice caused an electrical fire aboard an empty South West train, causing the suspension of services between Southampton and Waterloo