The Met Office has sent an urgent weather warning for fog on Sunday morning.
The yellow fog warning is in place from 6am until 11am, and covers huge parts of England, including London, the southeast, the southwest, and the Midlands.
Visibility could be cut to just 50m in some areas, although bursts of fog were forecast to come and go.
The latest weather alerts form part of a string of Met Office warnings for the entire weekend, owing to an Arctic blast pushing cold air toward the UK.
Yellow warnings for snow and ice are also in effect for most of the country until at least Monday morning.
The weather warning said: "Areas of freezing fog will come and go, but could produce very impaired visibility (down to 50 or 100 metres in places) as well as slippery surfaces this morning.
"Although becoming less widespread and less thick by lunchtime, some places may be affected through much of the day."
Some regions with particularly thick fog might find travel routes are disrupted, or at the least, slower than normal.
The Met Office urged the public to avoid travelling, if possible.
If you do decide to travel, you should drive slower than normal, and use dipped headlights - as opposed to full beams.
Freezing fog could also make the roads more slippery, so take extra care when driving in unusually cold weather.
Areas included in the yellow warning for fog include:
East Midlands
- Leicester
- Leicestershire
- Lincolnshire
- Northamptonshire
- Nottinghamshire
- Rutland
East of England
- Bedford
- Cambridgeshire
- Central Bedfordshire
- Essex
- Hertfordshire
- Luton
- Norfolk
- Peterborough
- Suffolk
- Thurrock
London & South East England
- Bracknell Forest
- Buckinghamshire
- East Sussex
- Greater London
- Hampshire
- Kent
- Medway
- Milton Keynes
- Oxfordshire
- Reading
- Slough
- Surrey
- West Berkshire
- West Sussex
- Windsor and Maidenhead
- Wokingham
South West England
- Gloucestershire
- Swindon
- Wiltshire
West Midlands
- Warwickshire
Meanwhile, snow and ice weather warnings were issued by the Met Office for Sunday, as large parts of the UK see snowfall over the weekend.
Parts of the country could see temperatures hit -10C on Monday morning, and travel is likely to be severely affected.
Roads have been blanketed by snow in the middle of Scotland, with snow ploughs needed to rejoin smaller communities with the rest of the country.
Snow was also reported in central parts of England, and is forecast to hit the southeast on Sunday morning.
