The energy regulator Ofgem has told ITV News that power networks could face fines if it is proved that they failed to respond quickly enough to reconnect customers left with no electricity after the storms at Christmas.
ITV News Business Editor Laura Kuenssberg reports:
Ian Marlee from the energy regulator Ofgem said it had been "dreadful" for many families and that Ofgem will now be asking the power networks to show they responded efficiently and quickly enough.
Marlee said there had been some good practice and it was "too early" to say if the power companies had failed in their duty to consumers. But added that Ofgem could take a range of action against the firms if they were found to have let consumers down.
At least 550,000 homes and businesses were affected by blackouts over the festive period, according to figures from the Energy Networks Association.
Some 100,000 properties were still without power on Christmas Eve, dropping to 24,000 by the end of Christmas Day as engineers worked around the clock.
Southern and eastern parts of the UK were affected for the longest time, but there were blackouts across the nation over the whole period.