Both countries are keen to increase their electricity supplies, with Belgium in particular needing new sources of power with five of its seven ageing nuclear reactors closed for repairs.

The 600 million pound Nemo project is being developed by National Grid and Belgian grid operator Elia.

It will enable up to 1,000 megawatts (MW) of electricity to flow between the countries, enough to power around one million homes.

"Nemo Link is the UK’s first interconnector since 2012, increasing our electricity capacity from these power cables by a quarter and further enhancing security of supply for us and Belgium," Britain's business and energy secretary Greg Clark said in a statement issued by National Grid.

The British power grid operator said it was investing more than 2 billion pounds in new interconnectors with Europe.

It plans to build a 1,400 MW link between Britain and Denmark, a second link with France and another link with Norway.

Britain already has power links with France, the Netherlands and Ireland, which bring in around 6 percent of its electricity.

Britain's government has warned operators of electrical power links with Europe that they will need to set up alternative trading arrangements if the country leaves the European Union next year with no exit deal.

(Reporting by Susanna Twidale; Editing by Mark Potter)