Heavy snow has led to power cuts and disrupted air, rail and road travel in many parts of the UK.
The deepest snow was in Sennybridge, near Brecon in Wales, where up to 30cm (12in) was recorded, while High Wycombe saw 17cm, and the flurries also reached London and southern England.
Snow is forecast to stay in Northern Ireland and Scotland but give way to icy conditions elsewhere overnight.
A Met Office yellow "be aware" warning for ice affects England and Wales.
A P&O ferry, the Pride of Kent, ran aground in high winds at Calais, in northern France. There were no injuries and the ship was refloated within two hours, although passengers were transferred to another ship.
Electricity supplier SSE says up to 24,000 homes in Oxfordshire, Berkshire and Wiltshire were left without power after snow and wind saw tree branches coming into contact with overhead network.
Across the South West of England and Wales, about 2,900 customers have been affected by power cuts. Western Power Distribution said it was hoping that number will decrease quickly as the weather eases across the region.
A campervan on the A40 near Sennybridge has been crushed by a falling tree. Dyfed-Powys Police said the road was closed between Llandovery and Halfway.
Elsewhere, drivers have been advised by police to avoid non-essential journeys.
Flights have been disrupted at several airports, including Heathrow, where snowploughs were used to clear the runways.
Heathrow remains open but says the de-icing of aircraft is resulting in some delays and cancellations.
Passengers flying into the airport have also said they are experiencing delays in disembarking from planes.
Buckinghamshire County Council says the majority of its schools will be closed on Monday because of the snow, while there have been similar announcements in Oxfordshire and Northamptonshire. Hertfordshire County Council says some of its schools have taken the decision to shut.
Schools in Birmingham will also be closed on Monday, while a Harry Potter event at the city's Genting Arena on Sunday evening was postponed after ticketholders concerned about travelling to the venue contacted the organisers.
There are no CrossCountry trains between Birmingham and Bristol due to fallen trees.
BBC Weather says a gust of 74.9mph was recorded by Devon County Council Highways on Taw Bridge in Barnstaple, which was closed to high-sided vehicles.
An amber warning for snow was extended on Sunday to cover Gloucestershire, Wiltshire, Oxfordshire, Buckinghamshire, Hertfordshire and Essex but areas such as Liverpool and South Yorkshire were downgraded to a yellow "be aware" warning.
Temperatures reached lows of -10C (14F) in some parts of Scotland and Wales, falling to as low as -14C (6.8F) in isolated rural areas.
The Met Office says ice is likely to be the "main hazard" over the next 24 hours as it issued a further yellow "be aware" warning for snow and ice in Scotland and Northern Ireland.
It warned of icy surfaces on Monday in Wales and in the Midlands, East of England, London and the South East, the North West, South West, and Yorkshire.
"Ice is expected to form across many places overnight into Monday morning. Some injuries are likely from slips and falls on icy surfaces as well as icy patches on some untreated roads, pavements and cycle paths," it said.
"As well as this lying snow from Sunday will continue to be a hazard leading to longer and potentially hazardous journeys."
It said some snow may fall over parts of Kent, Sussex, Surrey and Hampshire on Monday morning but it was not expected to settle.
Highways England has asked drivers to prepare for "any eventuality", making sure to have warm clothing, food, drink, required medications, boots, a shovel and a torch if venturing out.
The British Red Cross has also been asked to help move blood supplies and other medical equipment in some areas.
Heavy snow and rain is causing disruption across the UK, with many drivers being affected.
The A470 at Storey Arms in Powys, Wales, is shut
Heavy goods vehicles are advised not to use the A417 in Gloucestershire after a number of collisions between the A429 and A436 but the carriageway has reopened
On the M1 northbound, the road has reopened between junctions 16 and 17 after "numerous breakdowns/collisions"
Outside Warwick, the M40 was closed after a crash between junction 15 and 16 involving multiple vehicles but has since reopened
And between the Welsh border and the A5 near Shrewsbury, the A458 in Shropshire, police have reopened the road after an earlier crash
National Rail has warned of travel disruption on services in Wales, the Midlands, East Anglia, London, the Chiltern Railways network and South Western Railway trains.
All lines through Birmingham New Street will be disrupted until the end of the day.
Passengers travelling to and from Belfast International, Belfast City and the City of Derry Airport in Northern Ireland have been advised to leave additional time for journeys.
The runway at East Midlands Airport was closed for several hours causing delays to flights and some cancellations to Jet2, Flybe and Ryanair services.
Birmingham Airport had suspended flights so staff could clear snow from the runway.
Earlier, Luton Airport had to shut its runway and temporarily suspend flights and the runway at Stansted Airport, where about 50 flights were cancelled, had to be cleared.
Local events have also been affected by the weather, such as the final day of Lincoln Christmas market, which has been cancelled over safety concerns.
Photo copyright: REUTERS. Caption: The scene on the A40 near Sennybridge in Powys