The coldest reading was in the village of Sennybridge, Powys, on Wednesday morning with the lowest November figure since 2010.
Meteorologists also measured a temperature of minus 8.5C (16.7F) in Benson, Oxfordshire.
The Met Office is expecting slightly less chilly evenings for Wednesday onwards as clouds move down from Scotland, but the colder temperatures are likely to return at the weekend and some areas could still get a fair amount of frost, meteorologist Sophie Yeomans said.
In Scotland, there could be a few bright spells in some areas on Wednesday, but cloud cover in the west may be thick enough for patches of rain.
The Shetland Islands are expected to receive lengthy but light showers and gales are also forecast for the far north.
The middle band of the UK is likely to see fog patches in the morning around Gloucestershire, Oxfordshire and the Vale of York but they will clear to sunny skies as clouds move down from the north.
The southbound clouds are expected to lift the mercury slightly as they push down towards central and northern regions and elevate overnight temperatures slightly.
Ms Yeomans said conditions were slightly colder than the average daytime temperatures for this time of year but this could be the result of a temporary cold spell.
On Wednesday, London and Cardiff are expected to peak at 4C (39F), Glasgow to reach 9C (48F) and Edinburgh to head towards 8C (46F).
The colder conditions come as the Local Government Association’s (LGA) annual winter readiness survey shows that councils are well prepared for plummeting temperatures with a substantial stock of grit.
About half are at the limit of storage capacity, and the LGA said gritters will be out treating thousands of miles of roads whenever overnight temperatures drop below zero in the coming days.
LGA transport spokesman Martin Tett said: “We are well prepared for the cold, with 1.2 million tonnes of salt stockpiled and a fleet of state-of-the-art gritters ready to be deployed.”
Public Health England has warned people to remember that “cold does kill” even in places that are not experiencing the coldest temperatures.
December 1 marks the beginning of meteorological winter, which lasts until February 1.