Hundreds of schools are shut, some for a fourth day, as weather warnings including an amber alert remain in place across many parts of the country.

Much of the UK endured temperatures below freezing overnight, with preliminary data from the Met Office indicating the mercury fell to as low as minus 13.6C at Tulloch Bridge in the Highlands.

It comes after the UK had its coldest night of the winter so far on Tuesday into Wednesday, when Dalwhinnie in the Highlands experienced a temperature of minus 14C.

An amber warning for snow across northern Scotland, the Orkney and Shetland Islands is in place until 6pm on Thursday, with the potential for up to 20cm more snowfall.

All schools are closed on Thursday amid the wintry conditions in Orkney and in Shetland, where many have been shut since Monday.

More than 200 schools and nurseries are closed across the Highland region, around 130 are shut in Aberdeenshire and others had delayed openings, while in Moray nine schools and nurseries are closed due to the weather and others had late or staggered starts.

Other parts of Scotland and Northern Ireland have a yellow snow and ice warning spanning the whole of Thursday, while the north and north west of the UK are likely to see further wintry outbreaks over the next 24 hours.

Separate, shorter snow and ice warnings were in place for Wales and south-west England until 11am on Thursday, and in eastern England until midday.

A final yellow ice warning for south-east England, including Kent, Surrey and East Sussex, was in place until 10am.

Met Office chief meteorologist Jason Kelly said: “With deep snow already lying on the ground for many in the northern half of the UK, we’re going to see a significant topping up of totals over the next couple of days, especially for those in the north of Scotland.

“Within the amber warning area, an additional 15-20cm of snow is possible in a few locations.

“Strengthening northwesterly winds will also cause some lying snow to drift, potentially bringing some additional hazards, such as temporary blizzard conditions.”

Travel warnings are also in place across Scotland.

On the railways, ScotRail said its local stopping Dundee-Arbroath, Montrose-Inverurie and Inverness-Elgin trains will not run, while services between Inverness and Edinburgh/Glasgow will take 30 minutes longer.

Scotland’s transport minister Fiona Hyslop said: “We know from recent severe weather events that it’s important to plan ahead if you are looking to travel. With the Met Office issuing an updated amber warning for snow in the North Highlands and Northern Isles, travel planning becomes vital.

“Police Scotland is warning of a high risk of disruption for the parts of the country covered by the amber warning, but yellow warnings can also be impactful and cause delays. Please allow extra time for your journey and consider if it can be delayed until conditions have improved.”

She added: “Winter resilience plans have been in full effect with teams across Scotland working overnight to grit the trunk road network for essential journeys. Local roads may also be impacted, so please make sure your route is available, follow the travel advice from Police Scotland and drive to the conditions.”

National Rail warned the wintry weather could affect train journeys on Thursday.

In Northern Ireland, people have been urged not to travel unless it is “absolutely essential” because of limited gritting of the roads in zero-degree temperatures as public sector workers walk out in the biggest strike in the region’s recent history.

Another frosty night is forecast into Friday, and while it will be breezier with more cloud in places, lows of minus 10C will again be likely in some areas.

Wind coming in from the Atlantic in the west will then take charge through Friday and into Saturday, bringing much milder, wet and windy weather for the weekend.