Alexander Temerko, a major Conservative party donor, said he feared electricity market prices could jump by almost a third if the UK does not remain part of the EU’s internal energy market after a no-deal Brexit.

The Ukrainian-born billionaire, who is planning to build a new electricity cable between the UK and mainland Europe, said the price hike could mean higher bills and negative consequences for UK business.

Temerko publicly dropped his support for Boris Johnson during the Conservative leadership campaign earlier this year over fears he could steer Britain towards a no-deal Brexit.

“If we have a no-deal Brexit all existing regulations for the transmission of electricity will be terminated with immediate effect. I don’t know how quickly, or how high, the price of electricity would jump. My expert opinion is that prices could jump by 30%. But there are no scenarios for this. We are not ready,” he said.