A cold snap dubbed the "mini beast from the east" is set to arrive this weekend, with temperatures tumbling.
The Met Office has upgraded a previous warning for parts of London, the south east and across the Midlands to Amber - the second highest warning - amid fears of widespread disruption and injuries.
Up to 5cm (2in) of snow could fall in some parts of the country and up to 20cm (8in) on higher ground - prompting snow and ice warnings to be issued for the weekend.
Met Office meteorologist Mark Wilson said: "The best way to describe this is as a real return to wintry conditions.
"The last couple of days have been quite mild across parts of the UK - we got to around 16C yesterday in Wales - but by tomorrow all of us will be back to very cold weather.
"Bitterly cold is the best way to describe it - temperatures on the face of it probably just around freezing but with wind it's going to feel well below freezing."
The cold weather should only last a few days though - by Tuesday temperatures will be getting back to average for the time of year.
Meteorologist Martin Bowles said the weekend's weather could be dubbed a "mini beast from the east".
He said: "We don't expect anything like the same impact as a result of it, although there will be some snow about."
The Met Office warnings for snow and ice begin at 6pm on Friday for eastern Scotland and England, and run into all of Saturday where London and the South East are included.
The snow warning for Sunday shows vast swathes of the south, central and east of England covered by the yellow advisory.
The warning states that travel disruption is possible, rural communities could become cut off, vehicles may be stranded and power cuts may occur.