Motorists are being warned of icy roads throughout today after freezing temperatures overnight.
The Met Office says icy stretches on roads and pavements will be a problem throughout the day.
Driving conditions will be difficult with journeys likely to take longer than usual and delays to air travel are possible.
A chief forecaster for the Met Office said: “The fog will form initially, and will probably be most widespread, across parts of the southwest of England, southeast Wales and the southwest Midlands. Fog will also form elsewhere but areas of cloud are leading to uncertainty in the timing and extent of the fog and will result in the fog waxing and waning through the night and during Tuesday morning. However it is likely that some dense fog patches will develop in other parts of the warning area by Tuesday morning.
“The fog is expected to slowly thin and lift during Tuesday although it may persist in some areas throughout the day.”