Energy leaders have warned that household bills could rise by another 50% over the next six years.

The claim from the industry's trade body, Energy UK, came as EDF became the latest big six supplier to increase its current tariff by an average of 3.9% from January.

And it came as senior executives from RWE and another major power company said they believed that security of supply was more important than affordability.

Angela Knight, the chief executive of Energy UK, defended the sector and argued that the UK had the lowest gas price in the European Union and one of the lowest electricity costs. But she said the "old trilemma" of decarbonisation, energy security and affordability meant there was relentless upward pressure on prices.

"The industry has become a lightning conductor for the general concern about the cost of living. As a result we stand accused for things that we do, for things that we don't do, for things that we are responsible for and things that we are not … this is not an understood industry."

Knight then referred to a report from investment bank UBS that said: "UK household energy bills have risen 70% since 2004; we expect them to rise another 46% in nominal terms by 2020." Knight pointed out that UBS also blamed 95% of the future estimated tariff rises to government policies and power transmission network costs.

The UBS report was also endorsed at the conference by Andrew Wright, the chief executive of energy regulator Ofgem, although he quibbled with some assumptions on the network costs. Meanwhile Guy Johnson, a director at RWE npower, said he believed that energy security was the most important element of the trilemma mentioned by Knight. His position, in response to a question at the same conference, was endorsed by Benj Sykes, the UK country manager of Dong Energy. EDF is now the fifth of the big six to raise prices, announcing average gas and electricity price rises of just under 4%.

Mark Todd, director of price comparison website energyhelpline, said the move was in some ways welcome. "This is the lowest price rise so far at 3.9%, and is set to embarrass the four other big six players that have so far announced hikes averaging 9.1%. It highlights the difference between the companies, proving that they are not simply sheep bleating similar price rises one after another."