Hertfordshire Highway's 59 gritters have been out across the county more or less continuously since 3am. They have carried out three full runs overnight and used snow ploughs on the last run. Farmers have also been alerted to clear some rural roads with snow ploughs.

County Councillor Stuart Pile, executive member for Highways, Transport and Rural Affairs, said: "We are doing all we can to ensure the roads are as safe as possible, but motorists need to be particularly careful.

"There are some basic steps that everyone can take to keep themselves safe and comfortable - keep essential items like boots, blankets and a shovel in your car; you never know when you might need them.

"Driving conditions will inevitably be more difficult in bad weather and drivers should take extra care. In extreme conditions, only drive if you really have to."

Hertfordshire Highways salt the county's A and B roads, all bus routes, at least one road in and out of villages, industrial areas and shopping centres. Around 300 tonnes of salt is used on each outing but in extreme weather conditions, up to 2,000 tonnes a day could be spread on the county's roads.