Cross-border interconnection allows countries to supplement their own domestic generating capacity with imported power when supplies are tight, and to export surpluses when demand is higher elsewhere. 

The EU’s internal energy market ensures that electricity can be traded seamlessly, without tariffs or regulatory hurdles. The same applies to gas supplies via cross-border pipelines.

But uncertainty over the future terms of cross-Channel trade in electricity has raised doubts over billions of pounds of planned investment in increased interconnector capacity.

One of the proposed Anglo-French interconnectors is being developed by a company called Aquind, whose investors include Alexander Temerko, a Ukrainian-born British industrialist and large Conservative party donor. He says his project will go ahead irrespective of Brexit but wants Mrs May to raise the issue of energy trading when she meets Mr Macron at the Sandhurst military academy in Berkshire on Thursday. “Technically, our project is very important for the EU as well as the UK,” says Mr Temerko. “Brexit doesn’t change the economic or technical case for interconnection, but politically it is not good because it creates instability.”

Mr. Temerko also thanked the UK and French governments and their energy regulators for the constructive engagement so far and urged the officials in both countries to develop a common position on energy regulation as a part of the ongoing Brexit negotiations.