Temperatures dropped as low as -18C (0.4F) in Oxfordshire overnight on Wednesday, with further freezing temperatures expected.
The BBC Weather Centre said the village of Benson, near Wallingford, saw the lowest overnight temperature in the UK.
However temperatures could plummet to -20C (-4F) in parts of the south later, setting new local records.
More than 250 schools remained closed on Thursday and were expected to be shut on Friday.
The British Red Cross has sent emergency teams into Oxford to visiting vulnerable people.
The Oxford Mini car factory was closed on Thursday morning, but production was restarting with the late shift.
Many rural bus services remain cancelled or were running on revised routes.
The Oxford Radcliffe Hospitals NHS Trust has said its hospitals were now open, and most services are running as normal, with some exceptions.
It advised patients to check its website or ring the hospitals.
Oxfordshire County Council has said its gritters are now starting to go off the main routes to try to ensure access to more rural communities.
The county is on a priority list to get more grit and salt delivered.
The council added some schools would reopen on Friday, but this was likely to be the exception rather than the rule.
Oxford City Council said it had been continuing to grit priority roads and its 4x4 vehicles had been rescuing stranded vehicles at Shotover Country Park.
All city council sports games have been cancelled this weekend.
Park staff are also dealing with dangerous trees in Hinksey Park and are keeping the birds warm and fed at the aviary in Cutteslowe Park.
Some bus services ran in the county on Thursday, but mostly on main roads.
Trains were also hit, with First Great Western cancelling service between Oxford and Bicester.
The United Kingdom Atomic Energy Authority, in Culham, told its 1,000 staff and contractors not to come to work.
Oxford Brookes University closed non-essential buildings and services.
South Central Ambulance Service said it had received 43 emergency maternity calls on Wednesday, compared with 14 on a normal day.
It added it had been reaching patients in 4x4 vehicles.
Benson was only two degree celsius warmer than the South Pole, where temperatures dropped to -20C (-4F) at the Amundsen-Scott South Pole Station in Antarctica.
Wintry conditions in Oxfordshire are expected to last until the weekend as temperatures remain at or below freezing.