Much of the UK including London was expecting snow and ice on Monday after being hit by storms throughout Christmas.
The Met Office has put in place yellow weather warnings for snow and ice across Northern Ireland, most of Scotland and much of Wales.
A warning is also in place for snow and ice for England from the north-west down through the Midlands and across to Taunton in the west and London in the east.
Londoners are likely to wake up to temperatures of 0C (32F), with a maximum of just 5C (41F), while the mercury is expected to reach the same high in Cardiff.
The forecasting department said the rain moving across Wales and England in the early hours of Monday has the potential to turn to snow.
Snow had already fallen in parts of Scotland, Northern Ireland and England by Sunday afternoon, while more than 100 flood warnings were in place across England following days of stormy conditions.
The yellow warnings from the Met Office, in place from midnight until 6pm on Monday, advise of the potential for injuries from icy surfaces and delays to trains and road transport.
The chilly temperatures follow several days of wintery weather over the Christmas period which brought flooding to parts of southern England before Storm Bella arrived on Boxing Day with winds of more than 100mph.
Flooding was also reported in parts of eastern England by Sunday morning, with kayakers taking to the roads in Norfolk in an attempt to traverse water-logged streets.
As of 4am on Monday, 103 flood warnings remained in place across England calling for immediate action ahead of expected flooding, alongside 193 flood alerts.
Despite the bad conditions, gales meant that for the first time ever more than half of Britain's electricity was generated by wind power on Saturday.
According to energy firm Drax, 50.67% of the country's power was produced by wind turbines on Boxing Day.