Blankets of freezing fog and sub-zero temperatures are set to hit parts of the country.
Temperatures could be close to freezing in the coldest spots on Thursday, and some regions could wake up to "visibility at or below 100m because of the dense fog", said Met Office forecaster Mark Wilson.
A fog warning covering swathes of east Wales, the Midlands and eastern England is now in place, as areas across central and southern England have dealt with patches of fog and plunging temperatures.
Travellers should expect difficult driving conditions, longer trips and possible delays to their flights on Thursday.
A Met Office spokesman said: "Combined with temperatures below freezing, there is also the risk of ice forming on some untreated surfaces early on Thursday morning.
"The fog patches are expected to slowly thin during Thursday, although some patches may persist throughout the day - most likely in a zone from the West Country to eastern England."
Dozens of flights were delayed or cancelled due to poor visibility at London City Airport on Wednesday morning, while a string of arrivals were diverted elsewhere.
A major crash on the A40, which killed one female driver and injured around a dozen others, happened after foggy conditions made it "really dangerous", one witness said.
A motorist on the A40 who witnessed the fatal pile-up said that the poor visibility meant it was difficult for cars to see each other before they were "on top of it".
Public Health England (PHE) issued advice for the over 65s, those with long-term illness or who are not mobile.
Dr Thomas Waite, consultant in extreme events and health protection at PHE, said: "The effects of cold can be severe, in particular for those who are over 65, have a long-term illness, or are not mobile. Our advice to these groups is when indoors, have plenty of warm food and drinks and try to maintain indoor temperatures to at least 18C.
"If mobility isn't an issue, keep active as best you can. If you need to go out wear lots of thin layers, and shoes with a good, slip-resistant grip to prevent any accidental falls. It is particularly cold at night this week, so drawing the curtains at dusk will keep the heat in."
He also stressed the importance of checking on potentially vulnerable family and friends during the cold period.