Utilities stocks were under selling pressure on Monday after the UK Energy Secretary raised concerns about profit margins at the country's largest energy companies.Shares in British Gas owner Centrica were the hardest hit after Ed Davey ordered a regulatory probe into high household bills and suggested the company could be broken up.The stock was 2.43% lower at 306.55p by 13:24, having touched a 52-week low of 302.33p earlier in the session.Davey said margins made by the "big six" energy companies were higher than previously thought and singled out British Gas as it had charged among the highest prices to domestic customers in the last three years.He has written to energy regulator Ofgem as well as the Competition and Markets Authority, asking them to consider all possible remedies "including a break-up of any companies found to have monopoly power to the detriment of the consumer".Britain's Coalition government is facing pressure to force energy companies to cut high household energy bills after the opposition Labour Party pledged to freeze bills if it wins next year's General Election.Others in the sector, including Severn Trent and SSE were also trading lower this afternoon.Top performing sectors so far todayOil Equipment, Services & Distribution 21,887.10 +1.78%Industrial Metals & Mining 1,099.49 +1.52%Technology Hardware & Equipment 1,103.84 +1.35%Personal Goods 24,373.91 +0.91%Tobacco 33,607.68 +0.89%Bottom performing sectors so far todayElectricity 9,038.12 -0.98%Gas, Water & Multiutilities 5,538.63 -0.73%Financial Services 7,602.19 -0.35%General Retailers 2,731.53 -0.35%Travel & Leisure 7,283.00 -0.24%BC