A fog warning has been issued for Oxfordshire, with mist affecting large parts of Oxford.
The Met Office also issued alerts covering a substantial area of south-east England, including London, Brighton and Oxford.
Abingdon and Thame were among the Oxfordshire locations experiencing mist on the morning of Saturday, November 7.
The Met Office said the fog formed on Friday evening and had become dense in some areas, with visibility falling below 100 metres in places.
The conditions were expected to cause longer journey times, with possible delays to bus and train services and a chance of disrupted or cancelled flights.
The warning was due to remain in force until 11am, while temperatures were not expected to exceed 10°C.
According to the Met Office, the fog would gradually lift during Saturday morning and give way to mist and haze.
Conditions were expected to persist for longer in locations where visibility was initially poorest.
Drivers were advised to check road conditions, allow additional travel time and adjust plans where necessary.
Travellers were also advised to ensure fog lights were switched on and functioning before departure, and to check for updates from transport companies because bus, train, flight and ferry services could be affected.