The French energy giant EDF today finally decided to go ahead with Hinkley C . It may be a disaster for the largely state-owned company. If the British government now gives the nod to the first round of subsidies, it will surely be a disaster for British energy policy. This is not an untested model – worse than that. Its two sister stations, currently under construction in Finland and France, are overdue and over budget. Hinkley is predicted to cost £18bn to build, and it will cost consumers upwards of £30bn to run. It will displace billions of pounds of investment that could otherwise be spent reducing demand and developing renewable alternatives. The new prime minister and her ministers at the Department of Business and Energy, Greg Clark and Nick Hurd, should use the prerogative of a new government: stop it, now.

The justification for Hinkley C, originally conceived under Labour in 2008 and signed off by the coalition in 2011, is that when it finally comes on stream, perhaps in 2025, it will provide a large amount of carbon-free energy generation – 7% of total demand, which cannot be met by the weather-dependent energy that comes from renewables such as wind or solar. It will be a vital contribution to the UK’s low-carbon energy target. It looks like a bold solution to a big problem.

But it is not. The technology is too uncertain, and the scale is too large: so huge that it has been described as like building a cathedral within a cathedral. The construction costs are so great that EDF has had to be guaranteed a price for the electricity it generates that is higher than the cost of off-shore wind (which is expected to come down), and linked to the rate of inflation; to help finance it, the Chinese are providing £6bn and will own a third of the plant.

The government likes to suggest that there is no alternative. That is not what energy experts think. They point to different technologies, such as the Japanese-made advanced boiling water reactor, once scheduled to be built on Anglesey but now threatened by the voracious demands for cash of Hinkley C, or the US-made pressurised water reactor, the AP1000. The Chinese, keen to have viable European projects as a calling card for their own nuclear industry, may build modular reactors in East Anglia.

Better than any of these nuclear options, however, would be investment in renewables. Technology for tidal energy that will come from projects like the lagoons at Cardiff and Swansea is maturing. One of the world’s largest proposed wind farms, at Dogger Bank, off the north-east Yorkshire coast, could challenge the output from Hinkley C. More extensive interconnection with France, Norway and Denmark could smooth supplies. Most effectively, an investment of less than £1bn a year in domestic and industrial energy efficiency would halve demand by 2050.

Hinkley C has been repeatedly delayed by the EDF board in Paris; the unions think it will jeopardise their jobs. Two directors have resigned in protest. The project has been staggering along for years. Governments always fear changing their minds. But Theresa May says she wants to do things differently. She should start here.

• This article was amended on 29 July 2016. An earlier version referred to Iceland where Finland was meant.