The energy companies declared profits comes after they have stripped out costs for maintenance, development and investment costs. It also rather conveniently glosses over the massive profits most of the big 6 make being wholesalers/producers of energy - profits backed by government guarantee. And those profits can be in the order of 20% or more.
The amount of profit on domestic energy bills varies quite significantly also; Average profits back in April, for instance, worked out at around £100 per household or around 7% profits. This is remember, over and above they have taken out the green levy, taken out VAT, taken out the set-aside for investment and development. Infrastructure maintenance is already factored into their costs.
And lets not forget - Whenever the wholesale price of gas goes up, the retail companies immediately pass on that price rise; When the price falls dramatically, as it did in 2011-2012, that price reduction is rarely passed on.
We, the consumers, pay for all of this. We effectively pay for the cost of 6 competing sales and marketing operations, 6 lots of shareholders and dividend payments, 6 boards of directors salaries and bonuses, 6 customer service operations and infrastructure, 6 hierarchies of middle management, and all the evidence suggests we get precious little benefit that a market is supposed to produce - because the market is broken.