An ice warning covering much of the south-east will remain in place until 11am on Tuesday after snow, ice and fog brought widespread travel disruption to parts of the country. While Scotland experienced the lowest temperatures, with the mercury dropping below -15C, transport problems were greatest in the south-east. The first inches of snow to fall this winter left motorists negotiating treacherous roads and some rail services out of action, as airports cancelled flights after ice and fog closed runways. The Met Office said cold weather would persist through the week, and issued a yellow snow and ice warning for northern Scotland and north-east England from midnight on Tuesday until noon on Thursday. The Met Office said there would be heavy snow in parts of the north and Scotland on Tuesday, with as much as 8 inches (20cm) accumulating over high ground, and the potential for temperatures in northern Scotland to fall even further than the -15.7C recorded in Braemar, Aberdeenshire, overnight on Sunday. Milder conditions were expected by the weekend, although a Met Office spokesperson said the outlook remained uncertain. Drivers and rail passengers in the south-east in particular were left struggling on Monday as the wintry conditions closed major roads and rail routes in the early morning. National Highways said it had reopened all motorways in the south-east before lunchtime after many routes, including the M25, had been blocked in places by snow and accidents. The UK’s busiest motorway, orbiting London, was snow-covered in parts and closed entirely for several hours between junctions 23 and 25 in Hertfordshire because of jackknifed lorries. Gritters, snow ploughs and emergency services were deployed to reopen all roads in the region. National Highways said it had up to 25 gritters treating the M25 as snow and ice hit overnight, spreading 960 tonnes of salt and more than 18,000 litres of anti-freeze. The agency urged motorists to continue driving with care because of icy conditions. The AA president, Edmund King, said the number of breakdown callouts was about 25% higher than normal. On the railways, the wintry conditions mainly affected services in the south-east, after several inches fell around London, Anglia and Kent. Southeastern trains issued a “do not travel” warning on Monday morning and there was also significant disruption on services run by Greater Anglia, South Western Railway and Southern, ahead of strike action due to begin on Tuesday. Network Rail said it was deploying de-icing trains to treat tracks, especially in the south-east where the electrified services rely on the third rail. It said the first early morning trains were likely to be most affected by freezing weather. Early train services were disrupted around Edinburgh when icicles in a tunnel caused signalling failure. All East Midlands Railway trains were delayed due to a freight train having derailed at low speed and blocking the line. Tube trains in London were delayed and disrupted, particularly the outer network as ice and snow caused equipment failures on several lines. Network Rail said most services around Britain outside the south-east were otherwise running normally, on the first day of a new weekday timetable, after the official changeover of schedules on Sunday. More than 300 flights due to serve UK airports were cancelled across Sunday and Monday, with Heathrow, Manchester, Luton and Bristol among those affected. Gatwick and Stansted airports temporarily closed their runways on Sunday to clear snow. Gatwick was the worst affected, according to data from Cirium, cancelling 91 flights at the weekend and dozens more on Monday morning. Police warned people to continue to avoid open water after three children died after being pulled from a lake in Solihull in the West Midlands on Sunday afternoon after falling through ice. Richard Stanton, the area commander for West Midlands fire and rescue service, said: “We know the weather forecast for the next few days is expected to be bitterly cold. Please, adults and children alike, stay away from open water. Under no circumstances venture on to ice regardless how thick or safe you think this ice may be.”