Temperatures have fallen as the much-anticipated "big freeze" arrives with an Arctic blast.
Drivers have been warned to take care in snowy conditions
The cold snap is forecast to spread south bringing snow showers to much of the UK by Tuesday, the Met Office said.
Temperatures dropped to minus 6C in Katesbridge, Northern Ireland, and minus 5C in Redesdale, Northumbria.
Seven inches of snow was reported just south of Inverness on Sunday and even the south east of England is expected to get a couple of inches.
Two people were killed in a road accident in icy conditions at Mallusk, on the outskirts of Belfast early on Monday.
The Met Office said there was a chance of snow for the whole east of Scotland and England, with icy conditions in the west.
Drivers are being warned to be careful in what are expected to be tricky driving conditions.
The Highways Agency, which was criticised last year after thousands of drivers were trapped by snow on the M11 and M25, says it is ready for action.
A spokesman said its procedures had been streamlined to make sure gritters were on the roads in time this year.
It has 800 on-road weather information stations feeding the exact temperatures back and also has thermal mapping technology to help get gritters to the right places.
"We have the second most advanced system in the world - behind Japan - for predicting weather conditions.
"But last year we found the way we made the decision to grit the roads was flawed," a spokeswoman told BBC News Online.
"We have streamlined those procedures so, although people will see the gritters out as usual, behind the scenes things have changed."
Timing was crucial, she added, because if the gritters went out too early it would not be as effective.
The agency, which is responsible for motorways and other major roads, has 700 snow ploughs and blowers on 24-hour standby and 500,000 tons of salt ready to use.
Last year, it blamed heavy traffic for stopping its contractors from spreading grit on the M11, leading to huge tailbacks and drivers abandoning their vehicles.
Meanwhile, hundreds of airline passengers were left stranded at UK airports after snow and strong winds in Europe and north America grounded flights.
British Airways cancelled 20 flights, all from Heathrow and Gatwick, including two flights to Glasgow.
The bad weather has hit the snow-bound airports on the north east coast of America and across western Europe.
The flights cancelled were to New York, Washington DC, Paris, Toulouse, Geneva and Amsterdam.