Heavy snowfall has hit parts of the UK, causing road and rail disruption.
Amber weather warnings of more snow and very low temperatures are in place for Tuesday, and police say driving conditions are "treacherous" in places.
The M20 in Kent was blocked by stranded lorries, hundreds of trains are cancelled and some schools are closed.
Kent, Surrey, Suffolk and Sussex are among the worst-hit counties, seeing 5-10cm of snow, while north-east England has received up to 8cm (3in).
Temperatures dropped well below freezing overnight, with Northern Ireland, south west England and East Anglia logging figures as low as -6C.
Altnaharra in the Highlands recorded -8.5C overnight.
The UK is experiencing what's expected to be the coldest week of the winter, with snow sweeping westwards during Tuesday, increasingly moving into Scotland and the Midlands later in the day.
By Wednesday night, more than 20cm could have accumulated in some parts of eastern England and Northern Ireland.
Overnight, rail operators were running empty trains to keep tracks clear of snow.
However, hundreds of trains have already been cancelled as people attempt their morning commute.
Southeastern has cancelled more than 100 services, with trains from Kent to London Victoria and Cannon Street affected. There have been signalling problems between Tunbridge Wells and Hastings, and cancellations to early morning trains between Sittingbourne and Sheerness
Greater Anglia is running a limited service with fewer and slower trains between Norwich and Ipswich, and cities like London and Cambridge
Greater Northern said fewer trains will be running between Kings Lynn and Cambridge in the morning, services between Kings Cross and Ely have been cancelled
Tfl Rail will not start services until 7am, and will run a limited service between London Liverpool Street and Shenfield
c2c in Essex is running a limited timetable and customers have been advised to check the revised timetable before they travel
Southern is running an hourly service on its London Bridge to Uckfield line with additional coaches
Motorists are being urged to take extra care and in worst affected areas, to only travel if really necessary.
Emergency shelters have been opened across the country as councils offer extra accommodation to the homeless during the freezing conditions.
The offer of a hot shower, clean clothes, food and a bed can help save lives, homeless charity St Mungo's said.