A blanket of snow is set to cover Britain on Friday with up to 12in (30cm) falling on higher ground, amid fears the latest bout of wintry weather will bring the transport network to its knees.
The most severe weather is expected in Wales where a red alert has been issued, while the Met Office has issued an Amber alert for Northern Ireland and England.
Temperatures are expected to remain below zero in large parts of the UK on what is predicted to be a particularly “messy” day for travel.
Blizzards and strong winds are set to make conditions treacherous on the roads and motorists were warned heavy snow would arrive before the morning rush hour.
South West Trains has already announced changes to its services and will be operating a revised timetable on a number of routes on Friday.
Dumps of nearly 12in (30cm) are possible over the hills, a Met Office spokesman said.
The warnings came as police said a pensioner who was found dead in the street near his home may have collapsed while clearing snow from his driveway.
Graham Clark, who was in his 70s, was found with serious head injuries in the village of Buxhall in Suffolk on Tuesday afternoon.
The arctic conditions are expected to set in overnight, hitting Wales and the South West before pushing across the UK.
Laura Caldwell, a forecaster for MeteoGroup, the weather division of the Press Association, said 4-6in (10-15cm) is predicted to fall quite widely.
“Parts of the West Country, Wales, the West Midlands and central and southern England are going to get quite a bit of snow tomorrow,” she said.
“There will be quite a few centimetres in the morning with up to 10cm falling through the day.
“That snow will carry on, pushing north and east so it will cover all of England by the end of the day and even parts of southern Scotland.”
While Wales and the Midlands are expected to see the worst of the snow, London and East Anglia are likely have accumulations of around 4in (10cm).
Ms Caldwell added: “It’s going to inevitably cause disruption on the roads and railways. It’s going to be a bit of a messy day for travel.”
Forecasts suggest daytime temperatures will struggle to get above freezing in many areas, with the wind chill making it feel even colder.
The snow is expected to ease off later in the day, remaining largely in eastern areas.
But it is likely to stay very cold over the weekend.
The PSNI has issued the following advice to motorists:
• Slow down and leave plenty of room to stop. You should allow at least three times more space than usual between you and the car in front of you
• Brake gently to avoid skidding. If your wheels start to lock, ease off the brakes
• Turn on your lights to increase your visibility to other motorists and always clear all ice and snow off the car windows before setting out
• Drive slowly on snow in the highest gear possible.
• Never overtake snowploughs or gritting lorries. The drivers have limited visibility, and you’re likely to find the road in front of them worse than the road behind
• Do not assume your vehicle can handle all conditions. Even four-wheel drive vehicles can encounter trouble on winter roads.
Police would also advise for anyone unlucky enough to get stuck in snow:
• Do not spin your wheels. This will only dig you in deeper. Turn your wheels from side to side a few times to push snow out of the way.
• Use a light touch on the accelerator to ease your car out.
• Use a shovel to clear snow away from the wheels and the underside of the car.
• Pour sand, gravel or salt in the path of the wheels – or even your foot mats - to help get traction.
• If you must leave your car, arrange to have it recovered as soon as possible. If you think it is in a place that may pose a danger to other road users, call the police to let them know.
Police would also advise motorists to be mindful of the security of their vehicles. In a cold spell motorists, in an effort to de-ice their vehicles or to warm them up, have a tendency to switch the engine on and leave the vehicles running. This is a gift to nearby opportunistic thieves who just jump into the vehicles and drive off.
While it is good practice that all windows should be thoroughly thawed and cleared before driving Police would advise motorists to sit in the vehicle for the few minutes it takes to clear windows and heat the interior. Drivers should not switch their engines on and get out to scrape the exterior of their vehicles as cheeky thieves could take this opportunity even though the owners are close by.