In an interview with the BBC, Iain Conn said this is worrying as Britain is working to build its post-Brexit future on free trade.
I'm the first to admit that the UK market is not perfect. I just don't think that capping prices is the right way to help the market and it probably will have unintended consequences.
I think there are some at the heart of government who just don't believe in free markets and I find that concerning at a time when this market is highly competitive and the UK is seeking to forge a new future relying upon free trade with the rest of the world.
Shares in Centrica and fellow London-listed utility SSE tumbled more than five per cent yesterday after the Tories revealed their plan to reduce energy bills by capping prices. The plan was criticised by energy bosses and consumer groups as being ineffective and potentially increasing prices in the long run.
However, Greg Jackson, founder of challenger energy firm Octopus Energy, today backed the potential price caps.
Jackson said: "The energy industry has never been a free market. There are hundreds of pages of regulation, hugely influenced by the Big Six.
“A relative price cap would be the opposite of giving up on competition - it would unleash it. A simple 6 per cent relative price cap would be a better market-oriented solution. It’s simple to implement and would result in all consumers benefiting from competition."
May has praised free markets and free trade in the past, but she also said she is prepared to intervene in markets when necessary.