Hundreds of stranded drivers have spent a freezing night in their cars as thundersnow causes havoc over Britain, informs dailymail.co.uk.

Mountain rescue teams were drafted in to check on drivers stuck in their vehicles on the M74 in Lanarkshire after heavy snow showers struck the country, with up to 15in (39cm) of the white stuff hitting Dumfries and Galloway. 

All schools in the Scottish Borders have been shut today along with 200 in Northern Ireland, while commuters across Britain have been warned of treacherous conditions following the arrival of Storm Fionn over Ireland.

Severe 'be prepared' weather warnings were upgraded across the UK last night, with much of Scotland and Northern Ireland blanketed in snow and ice and drivers warned of lengthy disruptions during rush hour.

Ireland's national meteorological service has already designated the arrival of Storm Fionn, the sixth of the year, with a separate system bringing 80mph winds expected to hit Britain from tonight.

Traffic Scotland closed parts of the M74 in both directions - with tailbacks for six miles. Moffat Mountain Rescue assisted the operation to get the road clear by walking on the motorway and visiting drivers stuck in the tailbacks.

Sam Sykes, a surveyor from Biggar, South Lanarkshire, said he was stuck on the M74 for around 12 hours - from 6pm last night until around 5.30am today. He was travelling from Dalry in Ayrshire to Biggar, after work.

The 25-year-old said: 'It was really horrible as you would imagine. I was constantly checking the Traffic Scotland site for any updates but information was very limited. It wasn't really crawling, it was pretty much standstill for the entire time except a small period around 8pm when we moved a few miles.

'I got a little bit of sleep but the combination of cold and not knowing if you were going to be moving again restricted that.  The length of time, the cold and the uncertainty of when it would start again was the worst part. Luckily I am not in work this morning.' 

Mat Jackson, a product manager with Siemens, arrived home in Manchester at around 11.30am today - having left Glasgow at 3.20pm yesterday.

The 29-year-old, who was returning from a business trip with a colleague, said: 'Leaving Glasgow we were stood still for around four hours, moving maybe 300 yards in total.

'Every time gritters went by you thought 'here we go' but the snow just came down harder, it was that thick you couldn't see in front of you.

'People were driving on the hard shoulder, and crossing lanes and getting stuck in the drift, which was about a foot deep, compounding the mess.

'We didn't get properly moving until around 3.30am. I didn't want to sleep as the traffic might've started moving! It's completely screwed my sense of time, I'm out of kilter.

'Thankfully the boss has given me the day off work, so I'm away for a cup of tea and some sleep.'

Transport Minister Humza Yousaf apologised to those who had been stuck in their cars overnight.

He told BBC Radio Scotland's Good Morning Scotland programme: 'Let me give an apology to those commuters that would have been stuck for a number of hours in their vehicles, particularly on the M74, where it's been a really, really challenging night. 

'We knew of this, we've been warning of it since last week, we've been patrolling with gritters across the entire network but the depth of the snow, the amount of snow and the widespread nature of it frankly made it extremely, extremely challenging across the country.'

Asked if everything had been done in terms of gritting that could have been done, he added: 'Without a shadow of a doubt, I've double checked that as well throughout the night. We had hundreds of patrol vehicles and gritter vehicles out in the days before and during.'

Mr Yousaf said that if the road had been closed traffic would have been diverted off to local roads, leading to pressure on those roads as well.

He said: 'What we're trying to do is to keep the traffic flow going. What happened last night was that as soon as a patch of road was cleared, it was very clear that as soon as people started moving they lost traction again.

'In one incident alone seven HGVs were involved and we know that across the network over 50 HGVs have been involved in incidents too. So we're considering all options for the evening peak but also of course our immediate focus is to get the queues moving on the M74, but if there are other parts of Scotland that are facing challenges then getting them moving as well.'

Junctions 9 to 12 southbound and junctions 16 to 13 northbound of the M74 have been particularly affected by the snow with drivers becoming stuck on the road due to the 'challenging conditions'

Police declared a critical incident as they dealt with the situation on the M74 overnight and said more than 200 people were stranded. Chief Superintendent Stewart Carle told BBC Good Morning Scotland: 'The gritters are out.

'They are continually putting down more grit and ploughing, they are using heavy rescue vehicles to give jack-knifed lorries a tow to get them straightened up again.

'This will be a slow process and if the weather looks like it's going to turn again please listen in, we may give a message to say avoid travel on the M74.'

The force said: 'Partner agencies have been working together to ensure that welfare support is provided to road users who have been stuck on the M74. Officers from Police Scotland are urging motorists to avoid the area.' 

Borders Council said that all schools in the Borders would be closed today following heavy snow yesterday and overnight. It said the decision had been taken in the interests of the safety of pupils, staff, parents and carers.

It added: 'The council has considered all options in making this decision, and has taken it in conjunction with advice from partners, including Police Scotland.' 

Meanwhile 16 secondary schools, 58 primaries and 44 nurseries in the Highlands are shut today. Around 20 schools in Dumfries and Galloway and 28 schools and nurseries in South Lanarkshire are also closed. 

 First Minister Nicola Sturgeon also urged people to be careful, tweeting: 'The weather conditions will continue to be very difficult today. Please take care and follow advice from Police Scotland and Traffic Scotland.'