Britons brace for more travel chaos today as freezing fog rolls across the South following -3C chill overnight... after the Highlands enjoyed balmy 10C weather

Areas such as Salisbury hit -3C overnight but the Scottish highlands were 10.6C Cloud and fog in the south could mean buses, trains and flights are cancelled The unusual weather has 'flipped the norm' due to the pressure set up in the UK 

Britons are bracing for more travel chaos today as a freezing fog rolls across the South of England.

Temperatures plummeted to as low as -3C in Salisbury overnight as the Met Office issued a yellow weather warning for swathes of the South and urged Britons to prepare for busy roads and railways.

An overnight low of -8.6C was recorded in Benson, Oxfordshire, on Monday, whereas a comparatively balmy 10.6C was seen at Altnaharra in the Highlands.

The UK Health Security Agency has extended a level three cold weather alert until 9am on Friday, urging people to keep warm and check in on vulnerable family and friends.

Cloud and fog are set to cover the south as the Met Office issued a yellow weather alert

Britons are bracing for more travel chaos today as a freezing fog rolls across the South following a -3C chill overnight

Cloud and fog are set to cover the south as the Met Office issued a yellow weather alert and warned difficult driving conditions could cause travel delays in some areas.

The weather service said buses and trains could be delayed and there is also a chance of flight cancellations.

Met Office spokesman Oli Claydon said: ‘It’s relatively unusual – we obviously expect it to be the other way around, especially at this time of year, but, due to the position of high and low pressure around the UK, it’s flipped the norm.’

The Met Office has said the cold air across the south and much milder air further north is due to the ‘pressure set-up’.

It said higher pressure to the east is keeping things settled but cold in the south, whereas low pressure further north has allowed westerly winds to bring milder air in from the Atlantic, while further south ‘an easterly feed is keeping things cold with air in from the continent’.

Mr Claydon said temperatures will ‘start to even out’ by Wednesday but there will still be a ‘little bit of disparity’ with it likely remaining a ‘bit colder in the south’.

But he expects ‘more uniformity’ by Thursday, with temperatures of about 7C or 8C expected ‘across the board’.

The weather service said buses and trains could be delayed and there is also a chance of flight cancellations. Pictured: Foggy conditions on the A3 in Wimbledon on January 23

The Met Office has said the cold air across the south and much milder air further north is due to the ‘pressure set-up’. Pictured: A snow machine creates arctic conditions in Salford

Ely Cathedral in Cambridgeshire was shrouded in fog on Tuesday morning amid freezing temperatures

Frosty teasels in Bristol where clear misty skies on Tuesday morning brought frost across the south west

Deer graze during a foggy and misty sunrise at Ashton Court Estate, Bristol on Tuesday

It came as London Mayor Sadiq Khan issued a high air pollution alert for the capital yesterday.

Mr Khan said: ‘We all need to be careful over the next few days.

‘I’m urging Londoners to look after each other by choosing to walk, cycle or take public transport where possible, avoiding unnecessary car journeys, stopping engine idling, and not burning garden waste, all of which contributes to high levels of pollution.

‘This is particularly important in order to protect those who are more vulnerable to high pollution.’