Engineers have been drafted in from across the UK to help thousands of homes still without power following the destructive Storm Arwen.
The Energy Networks Association (ENA) said the number of UK homes powerless as of 5pm on Monday was 66,000, although around 1,000,000 homes and businesses are believed to have been damaged overall.
The worst-affected areas remain Scotland and north-east England, with engineers drafted in from Northern Ireland and southern England to help repair faults and “significant damage” to the network.
This comes as parts of the UK faced the coldest night of the autumn so far, including Shap in Cumbria, north-west England, which the Met Office said recorded the lowest temperature of the season so far at minus 8.7C (16.34F).
Prime Minister Boris Johnson pledged to help Scotland cope with the aftermath of the storm, which saw swathes of the UK hit by strong winds, sleet and snow over the weekend, while former Lib Dem leader Tim Farron called for the Government to bring in the army to assist.
The ENA said drone and helicopter surveys have revealed problems in hard-to-reach areas, with one patrol finding almost 100 electrical poles snapped and needing to be replaced.
An ENA spokesperson said: “Supporting and reconnecting customers is our absolute priority and our customer teams are working around the clock to contact customers and keep them informed.
“We are also working with other utilities, local authorities, emergency services and the British Red Cross to support this effort.”
Mr Johnson said the UK Government was standing by to help Scotland.
In a tweet, he said: “My thoughts are with those continuing to face any disruption caused by Storm Arwen.
“The situation in the north east of Scotland is among the most concerning and while forecasts are improving, we are on stand-by to provide further assistance to the Scottish Government.”
In the Commons, Mr Farron said “These people are facing their fourth night without electricity. We need support tonight to help the hard work of the engineers working around the clock to fix those connections, to increase their numbers. That may well mean bringing in the army.”
He added: “We also need support for the amazing community volunteers helping vulnerable people and families who are cold, hungry and suffering in other ways. After four nights without power, most people become vulnerable.”
In Wales, rail services will be affected this week as trains that ran over debris-littered tracks are repaired, Transport for Wales said.
The Met Office said cold temperatures will be replaced by a warming trend on Monday, followed by another dip in temperatures on Wednesday night.
Spokesman Oli Claydon said: “The whole of the UK will turn milder. The places that will hold on to the cold air the longest will be in the south-east of the UK.
“The low temperatures will return on Wednesday and Thursday night.
“However, I don’t think it will be quite as low as we have seen before.
“It will still be below zero, but more like minus 4C (24.8F) or minus 5C (23F).”
The London Ambulance Service (LAS) and charity Age UK have urged people to look out for elderly relatives who are most likely to suffer adverse health effects in cold weather.
Age UK advised people to keep moving and ensure they get their winter vaccines, while LAS urged people to check on their grandparents.
LAS said in a statement: “Please look out for family, friends and neighbours who may be vulnerable in colder weather.
“Just popping in for a cup of tea and making sure they are stocked with groceries and their heating is working could make a huge difference.”