Electricity firms must "up their game" following a critical report into the response to Storm Arwen, which left almost a million homes without power, the industry regulator has said.

Winds of 100mph uprooted 16 million trees and damaged power lines, cutting the electricity supply from November 26 last year across northern England and Scotland.

The watchdog Ofgem has released the findings of a six-month review and said some customers received "unacceptable service", with some cut off for more than a week, poor communication about when they would be reconnected and slow compensation payments.

Three network operators - Northern Powergrid, Scottish and Southern Electricity Networks and Electricity North West - have paid nearly £30 million in compensation and agreed to pay another £10.3 million in "redress payments" to local communities.

While acknowledging that engineers, supported by the Army, worked very hard in challenging conditions, Ofgem chief executive Jonathan Brearley said: "It was unacceptable that nearly 4,000 homes in parts of England and Scotland were off power for over a week, often without accurate information as to when power would be restored."

The Ofgem review found:

- Some affected customers remained off power for an unacceptable amount of time, received poor communication from their network operator and compensation payments took too long.

- Plans in place to deal with the storm were not sufficient to deal with the scale of the damage.

- Limited remote monitoring stopped firms from understanding the full scale and complexity of faults.

- There was some correlation between the age of electricity poles and how badly damaged they were in the storm, although this needed further examination.

Ofgem has recommended firms should submit their winter plans to the regulator, so it is sure they are prepared.

They should also stress-test their websites and call centres to ensure adequate capacity during severe weather events.

Firms should also develop systems to speed up mass compensation payments.

Electricity North West announced a multi-million-pound package of investment following its own review into Storm Arwen.

Read more: Network brings forward plans for £6million investment after Storm Arwen report

The power network has brought forward £5.2m of investment, to ‘improve and enhance’ its network and restoration systems, on top of the £140m which it spends on reliability and resilience each year.

The company has also announced that it is investing an additional £1.2m on systems to provide ‘more accurate’ information on restoration times, in direct response to customer feedback following the storm.

David Smith, chief executive of the Energy Networks Association, which represents the UK and Ireland's energy networks businesses, said firms have planned improvements.

He said: "This is particularly important as severe weather events become more frequent.

"The six electricity distribution network operators have submitted these details in their business plans for the next five years and Ofgem is due to make its initial determination in the coming weeks."

MP for Westmorland and Lonsdale, Tim Farron, said the report made 'important recommendations', but that it did not look into the role of central government.

“The report from Ofgem into Storm Arwen provides some very important recommendations in terms of making the network more resilient, and improving communications with people who have lost power," he said.

“However, I believe one of the key things missing from the report that desperately needs to be improved is the response of central Government.

“It took five days before a minister even came to the House of Commons to make a statement on the situation, which was symptomatic of a Government who did not act quick enough to get generators and support to people who desperately needed.

“Meanwhile on the ground, engineers and volunteers were working round the clock to help people in their hour of need."