The cold snap is expected to continue across the UK, with lows of -8C (17.6F) forecast for much of southern England and Wales.
Forecasters say temperatures could drop to -10C in rural Hampshire and Surrey and Bristol could dip to -6C overnight.
The mercury dropped to -11C in Aboyne, Aberdeenshire, and in Shap, Cumbria, on Monday night.
Britain's biggest pensioner group has warned that 12 pensioners could die every hour during the cold snap.
The prediction from the National Pensioner Convention (NPC) is based on official statistics, which show from December 2007 to March 2008 there were an extra 25,300 deaths in England and Wales compared with the average for non-winter months.
The NPC is calling on the government to double the winter fuel allowance to £500 for every household and introduce a industry-wide tariff for older customers.
"Since 1997, we have lost over 260,000 pensioners during the winter months because of cold-related illnesses, yet the government seems incapable of acting"
Joe Harris, NPC general secretary, said pensioners needed more money so they could avoid having to decide whether to "heat or eat".
"Since 1997, we have lost over 260,000 pensioners during the winter months because of cold related illnesses, yet the government seems incapable of acting," he said.
"Pensioners see rising fuel bills and are constantly worried about whether or not they can afford to put their heating on."
City lows
There are not currently any severe weather warnings in place, but drivers are still being urged to take care.
The RAC reported blackspots in the West Midlands and northern and south-eastern England.
There were school closures in several areas on Tuesday, including 20 schools across Wales.
Water from burst pipes flooded a classroom and caused the collapse of the staff room ceiling at Bourton-on-the-Water Primary, in Gloucestershire.
Meanwhile, police in south-west England urged drivers to delay journeys because of ice after seven crashes, including two multi-car collisions on the A38 at Harcombe Bends, Devon, and at Tideford, Cornwall.
Forecasters say temperatures in Scotland will rise throughout the day as cloud and rain spread southwards.
However, sub-zero temperatures will remain in the Manchester and Hull areas - and southern England, the Midlands and Wales face another freezing night.
Cardiff, Birmingham and Nottingham are due to suffer lows of -5C, with London dropping to -2C.
HAVE YOUR SAYGritters were out spreading thousands of tonnes of salt on roads across the UK throughout the night on Monday.
Also on Monday, motoring organisations reported a 100% increase in the number of call-outs they had received.
The AA said most of the extra workload came from home starts, with flat batteries being the most common problem.
Age Concern urged vulnerable older people to take extra precautions to stay warm and keep active during the cold spell.
The charity added that £5bn of benefits were still going unclaimed, although the government said 2.5 million cold weather payments had already been made.
BBC weather forecaster John Hammond explained that the current freezing conditions had been caused by Arctic air sweeping across Scandinavia and over the North Sea.
Temperatures are still a long way off the record low of -27C (-16.6F) in northern Scotland 14 years ago, and the current cold period is expected to ease later in the week.
Pensioners worried about high energy bills can call Age Concern's free helpline on 0800 00 99 66 for advice.
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