The party of Prime Minister Theresa May, campaigning to broaden its majority in a June 8 snap election, has said it would cap domestic energy tariffs, responding to voter discontent about energy bills that have doubled over the past decade.

The pledge sent the stocks of Britain's two biggest energy suppliers, Centrica (>> Centrica PLC) and SSE (>> SSE PLC), down by as much as 5 percent earlier this week as a price cap would hurt their revenue.

EnergyUK, the industry group representing more than 90 British energy suppliers and producers, urged politicians to emphasise policies that will help make the market more competitive.

"Ill-considered or poorly constructed regulation risks removing the competitive impetus that has driven the huge benefits seen in the market we have today," said EnergyUK Chief Executive Lawrence Slade.

The lobby group warned that further price regulation would create huge uncertainty and potentially put at risk some of the 180 billion pounds ($232 billion) of investments needed to modernise power stations and networks by 2030.

Centrica (>> Centrica PLC) Chief Executive Iain Conn said this week that a price cap proposal suggested some in May's government did not believe in free markets at a time when it is pinning its hopes on free trade once Britain leaves the European Union.

(Reporting by Karolin Schaps; Editing by Adrian Croft)

Stocks treated in this article : SSE PLC, Centrica PLC