(Refiles to add UK in headline)
LONDON, March 23 (Reuters) - Britain's big six energy companies will face the threat of break-up this week with their regulator Ofgem expected to announce its intention to refer the firms to the new Competition and Markets Authority (CMA), according to the Sunday Times.
The British newspaper said Ofgem, the body that oversees the gas and electricity industry, will stop short of an immediate referral, citing industry sources, with a likely one-month consultation on the move.
It said the CMA, which takes over from the Competition Commission next month, could break up the big six, made up of Centrica-owned British Gas, SSE, EDF Energy , RWE npower, E.ON and Scottish Power, forcing the separation of their power-generation and retail arms.
Energy companies have been in the spotlight recently, facing a backlash from the public and politicians over what they say are unfair price rises. Energy firms have blamed the hikes on rising costs and political interference.
The affordability of heating British homes shot to the top of the political agenda last autumn after opposition Labour leader Ed Miliband promised to freeze energy bills for 20 months if he won power in a 2015 election.
Ofgem, the Office for Fair Trading and the CMA have been carrying out an investigation into competition in Britain's energy retail market, looking at prices, profits and barriers to entry.
Ofgem declined to comment on the likely outcome of the investigation when contacted by Reuters on Sunday but said: "We are working with the CMA and OFT and will publish a report by the end of this month."
A Centrica spokesperson said: "As we've always said we believe the UK energy market is intensely competitive and works in the interest of consumers and the country, with energy prices amongst the lowest in Europe."
(Reporting by Neil Maidment; editing by Keiron Henderson)