Travellers are facing further misery as airports, roads and rail continue to be badly hit by snow in parts of the UK.
Gatwick Airport has reopened after being closed for two days due to heavy snow.
Southern and Southeastern train services in south-east England are severely disrupted, and at least 6,500 schools across the UK were closed.
Heavy snow warnings have been issued in England for the East Midlands, East, and London and South East.
The Met Office also has a warning of widespread icy roads in the South West.
Transport Secretary Phillip Hammond told the Commons he was doing everything he could to keep Britain moving, but his Labour shadow minister Maria Eagle accused him of "complacency".
The government said that "challenging" road conditions were making it difficult to supply fuel to some areas - even though the refineries themselves were operating without major disruption.
The Independent Petrol Retailers Association claimed that up to 500 independent petrol retailers in Scotland and the east of England risked running out of petrol and diesel by the weekend. Filling stations in rural areas away from the main trunk roads were particularly vulnerable, it added.
BBC weather forecaster Helen Willetts said there would be further heavy snow showers in eastern areas of the UK on Thursday evening, with ice being the major problem overnight.
Temperatures could plunge to as low as -20C (-4F) in parts of Scotland, northern England and north Wales.
Areas such as Northern Ireland and western Scotland are set to be the next affected by heavy snow into the morning.
The Association of Train Operating Companies (Atoc) said that at Thursday lunchtime 70% of normal services were running and 58% of those were on time.
Atoc chief executive Michael Roberts said: "Our priority for today and the coming days will be to get as many services as possible running.
"Staff will continue to work round the clock to keep as much of the network up and running as possible."
Mr Hammond said he had heard "far too many stories" of rail passengers being unable to obtain information about train services.
"With the amount of snowfall we've seen the last few days, some disruption to train services is to be expected," he said.
"But what is completely unacceptable is for rail passengers to be kept in the dark about what is happening with their services."
The transport secretary has written to the train companies to remind them of their responsibilities.
In other developments:
The AA said it had attended 10,500 breakdowns across the UK by 1500 GMT on Thursday, with the busiest areas in the the south coast of England.
An active search by mountain rescue team volunteers for missing fell walker Gwenda Merriot, 60, from Wiltshire, has now ended, but posters are being put up and hotels and B&Bs are being contacted.
She was last seen in Ambleside in the Lake District on Wednesday morning and there has been heavy snowfall since then.
Some 1,200 schools were closed in Scotland on Thursday, representing 45% of the total number of schools.
Some children in the north-east missed out on lessons for a sixth day and about 250,000 Scottish pupils had the day off.
More than 4,000 schools were closed in England.
One of the worst-affected areas of England is South Yorkshire, where snowfall of up to 30cm (12in) brought parts of the county to a standstill.
A total of 38cm (15in) of snow has fallen in Sheffield, the most recorded in December since records began in 1882.
Overnight, temperatures hit lows of -11C (12F) in County Tyrone and -14C (7F) in the north-western Highlands.