* Pre-tax margin at 106 stg for coming year vs 101 stg in June
* Ofgem says prices charged to customers for energy not falling (Adds more comment from Ofgem and Centrica)
LONDON, July 31 (Reuters) - Britain's energy providers will make 106 pounds ($179) before tax for each customer they supply with electricity and gas this year, energy markets watchdog Ofgem forecast on Thursday.
The annual figure, which Ofgem forecasts monthly, has doubled in the past year and is up from a June forecast of 101 pounds.
Actual profits will vary depending on consumption levels which are affected by the weather, especially for gas.
On Thursday, Centrica-owned British Gas reported a 20 percent drop in first-half operating profit to 455 million pounds after a mild winter.
British Gas expects to make an average profit after tax of 40 pounds per household bill in 2014, Centrica Chief Financial Officer Nick Luff said in a conference call.
British Gas is one of the country's "Big Six" energy providers which also include EDF Energy, E.ON , RWE's npower, Iberdrola's Scottish Power, and SSE.
Ofgem's forecasts look at trends in wholesale prices, consumption patterns, network costs and the cost of environmental and social schemes.
"These major costs (which) a typical large supplier incurs to deliver energy to an average household appear to be falling, but the prices charged for energy are not," said an Ofgem spokesman.
However, Centrica's Luff said Ofgem's price calculations can be misleading.
"These are theoretical models and can give an impression that is very different to reality," he said.
1 US dollar = 0.5925 British pound Additional reporting by Susanna Twidale; Editing by Jason Neely