[F]requent and often heavy snow showers are expected to continue through Thursday and overnight into Friday morning with further significant accumulations likely.
Long delays and cancellations on bus, rail and air travel could occur.
Roads may become blocked by deep snow, with many stranded vehicles and passengers.
Some rural communities might be cut off for several days.
Long interruptions to power supplies and other services such as telephone and mobile phone networks, could occur.
A Met Office spokesman said: “Snow showers will bring variable snow cover, but parts of northern England and Scotland are expected to see the most frequent snow showers.
“During this time, a further 5-10 cm of snow is expected quite widely.
“Where showers become organised though, most likely across Scotland and over the hills of northern England, some places are likely to have an additional 15-25 cm of snow.
“Strong winds will continue to lead to drifting of snow, and severe wind chill, while lightning could be an additional hazard, particularly near coasts.
“Although snow showers across northern England will ease somewhat with time, continued blowing and drifting of lying snow is likely.
“This warning has been updated to extend the validity period into Friday morning as well as to extend the area further south across more of northern England.”
