Settled snow has turned to treacherous ice and caused disruption on roads and railways across the country as forecasters warned of freezing temperatures.

The deep freeze has also seen hundreds of schools close, thousands left without power and flights delayed on Monday, including at Heathrow where passengers have complained of waiting hours for travel to be rescheduled.

The Met Office has extended its yellow weather warnings for snow and ice to cover vast swathes of the country, including London and the South East, much of the Midlands, Northern Ireland and Wales, as well as the eastern coast of England and northern and western Scotland.

READ MORE: Glasgow turns into stunning winter wonderland as city shivers in freezing temperatures

Forecasters warned that clear skies on Monday night could see temperatures drop as low as minus 15C (5F), potentially beating Sunday night's low of minus 11.6C (11F) in Chillingham Barns, Northumberland.

Heavy snow still lying on the ground, particularly around the Hereford area, has disrupted services on West Midlands Railway and Great Western Railway, while London Northwestern Railway trains to Milton Keynes from London have been delayed or cancelled.

Emergency services warned motorists to drive with caution, even on motorways, with icy slush on the M40 between junctions two and three causing a van to flip over following a collision with two other cars.

South Central Ambulance Service tweeted: "Three vehicle RTC this morning on M40 J2-3 nbd with @tvprp @Bucksfire @HighwaysEngland 4 pts, fortunately all minor injuries tho 1 to hospital for further treatment. Road conditions icy; lots of slush in lane 4 at scene of collision. #SlowDown #DriveToTheConditions."

READ MORE: Glasgow turns into stunning winter wonderland as city shivers in freezing temperatures

Western Power Distribution said engineers worked through the night to restore power to 99,500 homes in the Midlands, South Wales and South West but 7,000 customers were still without electricity, 6,500 of them in the West Midlands.

SSE said they restored power to more than 50,000 customers on Sunday but 800 in Oxfordshire and parts of Wiltshire remained without power at 8am on Monday.

Birmingham City Council was forced to cancel all council-run school and related transport services on Monday, the authority said.

More than 200 schools were closed in Gloucestershire, more than 300 in Staffordshire and more than 100 in Shropshire.

In Wales, 71 schools were closed in Flintshire, 11 in Wrexham and 49 in Denbighshire.

Met Office meteorologist Alex Burkill told the Press Association: "It was chilly in Chillingham Barns, but it wasn't the coldest night of 2017 - that was Saturday night when temperatures went down to minus 12.4C.

"We could well beat that tonight and could go as low as minus 12C and even minus 15C."

Met Office spokesman Grahame Madge added: "We are not expecting too much more in terms of fresh snowfall and the risk now transfers to ice.

"We have got fairly widespread clear skies, which will bring temperatures down and where there is lying snow, that creates an ice risk."

He said a weather front coming in from France would affect the east coast and South East, bringing with it wintry showers, and possibly snow, but he added it would be "nothing like what we've seen already".

READ MORE: Glasgow turns into stunning winter wonderland as city shivers in freezing temperatures

Even former England striker Michael Owen was caught out by the weather on Sunday night, with snow-laden tree branches covering his Bentley.

He said: "Not ideal at 5.30am when you've got a train to catch! Thought I was clever sheltering my car from the snow!"

Kenton Keithly, 65, of Woodland, California, was stranded in Newcastle after his connecting flight to Heathrow was cancelled on Sunday and he must wait until Tuesday to return to San Francisco.

He said: "Speaking with other passengers in the line last night, we all agreed that BA has learned nothing from seven years ago and Heathrow have failed to address the issue of having enough de-icers to cope with demand when needed.

"Britain obviously doesn't do well in winter. Everything breaks down."

A Heathrow spokesman apologised for the continued disruption and said: "Flights at Heathrow are disrupted today due to crew and aircraft being out of position following yesterday's weather.

"Before coming to the airport, passengers must check their flight status with their airline. If the status of your flight is cancelled, please do not travel to the airport, keep updated via the airline's website.

"The safety and comfort of our passengers is always our first priority and we are working closely with our airlines to ensure affected passengers are looked after.

"We apologise to those whose travel has been impacted and regret the inconveniences that have been caused."

Pete Williams, the RAC's road safety spokesman, said they were expecting 11,000 breakdowns on Monday, a figure which is 20% above the seasonal norm.

"Many motorists are waking up to what has been dubbed Black Ice Monday on the roads as treacherous ice and snow conditions have been compounded by plummeting temperatures overnight.

"Drivers are advised to consider whether their journey is essential or if they can delay it and travel later."

More than a foot of snow fell in Sennybridge in Wales which saw 32cm (12.5 inches) on Sunday.

READ MORE: Glasgow turns into stunning winter wonderland as city shivers in freezing temperatures

Eurostar also warned passengers of delays in both directions caused by the weather.

Their website said: "Our apologies to passengers travelling today from the continent to London St Pancras and vice versa.

"Due to the predicted adverse weather conditions in the UK and the rest of Europe, speed restrictions are put in place. This means that your journey could be affected and that the arrival time of your train might be delayed."

Public Health England urged people to check in on elderly loved ones and those with heart and lung conditions and recommended heating homes to at least 18C.

Flurries of snow were seen falling in central London on Monday afternoon.

The TUC called on employers not to force staff to make hazardous journeys into work, saying firms in areas of the country affected by the snowy conditions should have put out advice to their staff on what they should do when snow, ice and a lack of public transport prevents them getting to work.

Policies should also cover what parents should do if schools close and they have no alternative childcare, said general secretary Frances O'Grady, adding: "It is essential that employers don't force staff to make dangerous journeys for the sake of presenteeism.

"For many employees the bad weather will have made their commute virtually impossible, but thankfully many bosses now have 'bad weather' policies so staff know what is expected of them."

Breakdown cover provider Green Flag said it had received more than three calls every minute, over double the usual number for a Monday at this time of year.