Coastal regions and exposed communities are braced for chilling 60mph gales with hail, snow and thunder threatening to pile on the misery.
Local authorities have put gritters back out on the roads amid warnings for icy conditions over the next few days.
Thermometers are due to plunge to below freezing nationwide as a swathe of bitter Arctic air engulfs the UK.
Overnight lows of -5C (23F) are forecast for the north with icy winds making it feel closer to -10C (14F) in exposed regions.
Elsewhere will struggle to get muchabove 9C (48F) or 10C (50F) by day before the mercury drops to around -2C (28F) after sundown.
The Met Office has warned of icy gales along the east coast with “frequent snow” and icy roads threatening travel disruption.
It said Britain is wrapping up for a week of winter weather with strong winds and stormy conditions forecast into the weekend.
Spokesman Grahame Madge said: “Temperatures will be down below freezing everywhere overnight into Tuesday morning.
“Wintry showers especially over high ground will turn quite intense by Tuesday with hail and thunder also expected in places.
“Through the week it is remaining windy and cold with wintry showers turning heavier down to lower ground and gusts of up to 60mph in exposed parts.
“This is the theme for the rest of the week as cold Arctic air is pulled down from the north.”
Although the worst of the freezing blast will hit northern and coastal regions nowhere will feel anywhere close to spring this week.
Heavy snow is forecast in Scotland while flurries are possible as far south as the Midlands, London, Kent and the West Country.
Councils are preparing for the worst with gritters and staff back out on the roads to minimise disruption from the freak weather.
The Local Government Association (LGA) has urged people to keep an eye on elderly and vulnerable friends and neighbours as the cold bites.
Environment spokesman Cllr Martin Tett said: “Councils are fully prepared to protect residents and minimise disruption as temperatures drop this week.
“We are well prepared for the cold with 1.2 million tonnes of salt stockpiled and a fleet of state-of-the-art gritters ready to be deployed.
“But council staff can’t be everywhere.
“They rely on community-spirited residents to look out for each other.”
James Madden, forecaster for Exacta Weather, warned strong winds and snow could whip up blizzard conditions in parts of Britain.
He said: “The upcoming week will bring below average temperatures for the time of the year for many.
“Areas of low pressure will also bring a rather unsettled week for many, and some of this precipitation is likely to turn wintry as the low pressure clashes with the much cooler air in place across our shores.
“Thursday could bring some noticeable snow showers in parts as far south as London.
“Some parts across higher ground could also see some developing blizzard conditions as the unsettled weather will also be accompanied by strengthening winds at times.”
Experts say the cold blast is being driven by a freak change in high-altitude wind direction leading to a sudden stratospheric warming (SSW).
The phenomenon, which set in at the start of month, is being blamed for the chilly start to spring this year.
Temperatures will be well below average for the time of year with daytime temperatures of 15C more usual for the end of April.
Met office chief forecaster Will Lang said up to four inches of snow could hit high ground by the end of tomorrow.
He said: “Northerly gales will bring unusually cold air for late April across the UK on Monday and Tuesday.
“Northern Scotland will bear the brunt of the wintry showers, with some snow accumulations, mainly by night and over higher ground.
“Frequent sleet, snow and hail showers will continue to affect northern Scotland into Tuesday.
“While accumulations by day will be temporary and slushy away from the hills, snow showers will settle more readily later on Monday evening, overnight and early Tuesday.
“Five to 10cm [four ins] may accumulate on high level roads above 300m with some drifting in strong to gale force northerly winds.
“Please be aware of the risk of some difficult and unseasonal road conditions, and the possibility of some low impact travel disruption.”
Ladbrokes has slashed the odds on April and May turning out to be the coldest on record as the weather keeps bookies and punters on their toes.
Spokeswoman Jessica Bridge said: “Spring’s weather has been all over the shop this year, and it looks like May isn’t going to be much better.”