The lowest temperatures of 2014 for England, Wales and Northern Ireland were recorded overnight.
Katesbridge, County Down, hit -8.8C (16.2F). Benson, Oxon, fell to -7.6C with -6.7C at Pembrey Sands, Dyfed.
Latest figures show the UK's coldest temperature of the year so far was -9C in Cromdale, Moray, on Saturday.
Meanwhile a Met Office cold weather alert for northern England and the Midlands has warned of health risks for vulnerable people.
BBC Weather said Scotland saw temperatures fall to -7.7C in Braemar, Aberdeenshire, overnight from Sunday to Monday.
Weather and travel info
Benson had also previously held the record for the lowest temperature of the year in England when it reached -6.8C on 6 December.
Wales' lowest temperature of the year was recorded in Pembrey Sands, south Wales.
BBC Weather's Peter Sloss said the cold temperatures mean it is already colder now than it was during "a good chunk of last winter", from January to March.
Sunshine on Monday was expected to raise temperatures during the day, he added.
The record lows come as parts of the UK have already been hit by sub-zero temperatures and forecasters warned of further plunging temperatures over the next three days.
A sharp frost is expected in some areas of England and Wales on Monday night, with the UK experiencing similar temperatures to those seen on Sunday night, BBC Weather said.
The Met Office alert remains in place until 12:00 GMT on Wednesday.
The amber - level three - alert is one below a national emergency and indicates social and healthcare services should target "high-risk" groups, such as the very young or old, or those with chronic diseases.
A yellow - level two - alert is in place in the rest of England indicating social and healthcare services should be working to ensure they are ready for a period of cold weather.
How to drive in snow and ice
- Balance your speed - too fast and you risk losing control, but if you go too slow you risk losing momentum
- Start gently in second gear, avoiding high revs. Stay in a higher gear for better control
- Only use the brake if you cannot steer out of trouble
- Increase the distance at which you follow other vehicles
- Plan your journey around busier roads, which are more likely to have been gritted
- On a downhill slope, get your speed low before you start the descent, and do not let it build up
- In falling snow, use dipped headlights or fog lights, but switch off if conditions improve
- Read more about how to prepare your car