Wholesale power and gas prices rose last month, squeezing already tight UK electricity supply further, after the IFA1 interconnector was damaged by a fire in Kent, affecting half, or 1 GW, of its capacity.
The other 1 GW capacity was already offline due to planned maintenance which was later extended to Oct. 23.
After a detailed assessment, National Grid said extensive work was needed to safely return the IFA1 to service.
"We have been able to reduce the outage time of 1,000 MW of capacity at the IFA interconnector so that it will come back to service on 20th October, ahead of the 23rd October date we had previously published," the grid operator said in a statement.
The other 1 GW, which was affected by the fire, remains offline, with a partial return to service planned from 2022.
National Grid said it will being 500 megawatts (MW) back to service from October 2022 to May 2023, which will result in a total of 1,500 MW of capacity available going into next winter, with full capacity achieved by October 2023.
"We are completely focused on getting IFA safely returned to service as soon as possible and ensuring we are able to support security of supply," it added.
The IFA2 interconnector, a second link between Britain and France commissioned in 2020, is operating and not affected.
(Reporting by Swati Verma in Bengaluru and Nina Chestney; editing by Jonathan Oatis and Alexander Smith)