National Grid has given the green light to an £850m plan to build the world’s longest high voltage power cable between the UK and Denmark.

The energy giant’s long-awaited final investment decision means the 460-mile Viking Link project will begin importing Danish electricity from 2023, rather than 2022 as originally planned.

National Grid boss John Pettigrew said the project will help keep the company on track to grow the value of its portfolio of pipes and wires by between 5pc to 7pc over the medium term.

The power cable will be capable of powering over a million homes and is expected to earn National Grid £100m of earnings before interest, tax, debt and amortisation once it begins transmitting power beneath the North Sea.

The decision emerged as National Grid revealed that its profits for the first half of this year fell by 6pc to £1.3bn after a perfect storm of woes in its US business.

The power network operator was stung by US tax reforms and major costs of repairing storm-hit assets on the US North East coast.

National Grid’s US problems also include a spate of industrial disputes over fresh worker contracts which has led to a £97m lockout of 1,200 gas workers in the US state of Massachusetts.