Twenty three flood warnings have been issued across southern England by the Environment Agency, with travel disruption likely due to difficult weather conditions.
Flooding is expected by 3am for an area stretching from Ludgershall in Wiltshire down to Dorset and across to Somerset.
Flights could be cancelled and journeys delayed because of “freezing” fog in the region, the Met Office said. Commuters have been asked to prepare for longer journey times due to possible delays to bus and train services.
A yellow warning for fog was in place until 8am for an area stretching from Exeter to Oxford. Temperatures as low as minus 5C were recorded in Benson in Oxfordshire, Farnborough in Hampshire and Wiltshire’s MoD Boscombe Down.
South of the Wiltshire military site, at Bournemouth Airport, recorded an overnight low of minus 6C by 3:30am.
The Met Office said: “Freezing fog will lead to difficult driving conditions and could cause travel delays in some areas. There is a chance of delays or cancellations to flights.”
Dense fog could see visibility drop to below 100 metres in places, the forecasters added, warning drivers to be vigilant.
Fog over parts of Dorset, Somerset and Wiltshire will be dense at times overnight but should clear on Wednesday morning (25 January).
There is likely to be difficult driving conditions due to the combination of reduced visibility and untreated surfaces turning icy.
The Met Office said residents and commuters in Bracknell Forest, Buckinghamshire, Hampshire, Oxfordshire, Reading, Slough, Southampton, Surrey, West Berkshire, West Sussex, Windsor and Maidenhead and Wokingham would need to be mindful of the conditions.
The fog was also due to hit Bath and North East Somerset, Bournemouth, Christchurch, Poole, Devon, Dorset, Somerset, South Gloucestershire, Swindon and Wiltshire.
It comes as an unusual temperature divide has hit the UK, with parts of Scotland more than 10C warmer than London this morning (25 January).
In its UK forecast for today the Met Office said it would be a “cloudy start for many with some freezing fog over parts of southern UK at first”.
This will be followed by rain from Scotland moving southwards, reaching southern England in the afternoon, before then giving way to brighter conditions - although some showers will remain in the far north.
For tonight it says: “Early evening rain over southern England soon clears away southwards. Otherwise, clear spells and a dry, chilly night for many, but some showers in the far north.”
Meanwhile, Thursday will be mostly fine and dry with sunny spells, but some showers are expected in windier northern and eastern coastal areas.