Heavy snow has been falling in Wales this morning and more is set to blanket Britain, with chaos expected on transport networks in the coming hours.

Temperatures are expected to remain below zero in most parts, making it bitterly cold, while blizzards and strong winds are set to make conditions treacherous on the roads.

Rail operators South West Trains, Southern, Greater Anglia and Eurostar have already cancelled services or revised timetables to cope with any problems caused by the weather.

Passengers were advised to check with operators before travelling.

Airports and schools are likely to be closed as the snowfall sweeps into the country from the southwest through the day.

A rare “red warning” has been issued for parts of South Wales, meaning all non-essential journeys should be avoided.

Journalist Nazaneen Ghaffar said up to 30cm of snow could fall in South Wales, with blizzards and snow drifts in higher areas.

She said: “There will be heavy snow across Wales for most of the day, especially in south Wales where 20-30cm is expected.

“Southwest England can also expect snow, and it will continue spreading east into the Midlands, northwest England, central and southern England by this afternoon.”

Amber alerts are in place for parts of the Midlands, London and the South, the east of England, the North West and Northern Ireland.

Snow will later reach Scotland, northeast England, Yorkshire, Lincolnshire and East Anglia, she said.

And there will be little respite over the weekend, with up to 10cm of snow likely in northern and eastern England as well as Ireland and southern and eastern Scotland. Snow elsewhere will be lighter on Saturday but it will be bitterly cold.

Sunday could also bring persistent but light snow to southeast England and some flurries for Scotland.

The Highways Agency has issued an amber alert and has placed a 500-strong fleet of salt-spreaders, ploughs and snow-blowers on stand-by.

Greg Carstensen, service director for Hounslow Highways, told  they were well-prepared with roads in some areas already gritted the night before snow was expected.

However, he still urged motorists to “listen to the advice being given out on television and radio and make sensible decisions and only make necessary trips if the snow is really that bad”.

The AA said the greatest risk of disruption would be in Wales, the West Midlands, southern England and Northern Ireland.

Darron Burness, the AA’s head of special operations, said the morning commute was “likely to test man and machine”.

Those who decide to travel have been urged to travel prepared with a fully charged mobile phone, warm waterproof clothes, boots and a blanket, some food and drink, and have a torch, ice scraper, de-icer and a shovel.

There have been reports of panic-buying at shops in Derbyshire and Wales.

At a supermarket in Ripley every loaf of bread and all the bananas had been bought up. One customer reportedly went home with 20 loaves.

Heavy Snow Hits UK Video

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