Work on the Nemo Link began in 2015 and it is due to be completed by 2019.
But the route, under the English Channel from Kent to Belgium, not only takes it under some of the busiest shipping lanes in the world, but also through a wartime graveyard of wrecks and unexploded ordnance.
An undersea survey found 19 pieces of unexploded ordnance from the First and Second World Wars.
"It's mines normally, sometimes bombs dropped from aircraft, some are from the first world war. You find mines that are attached to the seabed still, mines that are floating around," said Nemo Link project director Mike Elmer.
The Royal Navy and their opposite numbers in France and Belgium have carried out controlled explosions on several bombs and torpedoes.
Petty Officer Scotty Eaton, a Royal Navy diver, who was sent down to check on one of the mines, explained some of the difficulties involved.
"The biggest challenge we found was the tides, they are unpredictable," Petty Officer Eaton said.
A two-ton bunker-busting bomb dropped by the US air force was detonated by the Belgian navy in June.
Inside view #nemoLink converter station @brugge for interconnector be — uk #eliacorporate pic.twitter.com/om0xZ1qZFr
— Marleen Vanhecke (@marleenvanhecke) July 5, 2017
A 14th century shipwreck, which was discovered in French waters, almost delayed construction until it was realized that it was not directly on the cable's route. Mr. Elmer said it was immediately flagged up as an archaeological wreck.
"As soon as they designate it as archaeology, a 100-meter exclusion zone is put through the whole thing," he explained.
The interconnector cable will follow an 80 mile route from Richborough, near Ramsgate in Kent, to Herdersbrug near Bruges in Belgium.
The link will be able to deliver up to 1,000 megawatts, enough to power 500,000 homes.
Fortunately the route of the link is several miles south of the most notorious wreck in the Thames Estuary.
The SS Richard Montgomery, an American ship, lies on the seabed just over a mile from the coast of Kent.
It sank in August 1944 while bringing 1,500 tons of high explosives from the United States to England to help in the war effort.
Map of shipwrecks around the UK 🗺️ SS Richard Montgomery still contains 1400 tons of TNT — no one can go within 1600ft of it #ships pic.twitter.com/gqmRX4baOT
— Gareth Alston (@gareth_alston) 30 July 2017
Its cargo included a variety of wartime munitions, including 286 giant 2,000lb "blockbuster" bombs, 4,439 1,000lb devices and 2,500 cluster bombs.
There have been fears ever since that it will explode but, because it lies just south of the main shipping lane, it has always been considered to be not worth disturbing as it would take years to disarm all its ordnance.
Britain currently has four interconnectors and eight more are under construction, including the Nemo Link.
The European Union recently announced significant funding for a similar cable linking France and the Republic of Ireland. It has been dubbed the "Brexit cable" because it is designed to reduce Ireland's dependence on Britain for its energy supplies.
