Asked about the profits of the British Gas owner Centrica rising by 11%, the Prime Minister's spokesman said:
What consumers and the industry expect is that the Government and the regulator should be working together to help families.
That's what we are doing and that's why the Energy Bill will enshrine in law the PM's desire that consumers get the best tariffs.
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The letter was signed by the CBI, British Chambers of Commerce, the EEF, the Institute of Directors and the Federation of Small Businesses.
A spokesperson said Rory Stewart's remarks were in line with the British government’s stated position.
The minister's intervention will come a week after Trump decertified the landmark agreement claiming it was not in the US national interest.