Regulator Ofgem said the ESO, run by National Grid, did not have "adequate controls" in place at the time to provide accurate 7-day ahead electricity demand predictions, which are used to generate and buy electricity.

Between April and October 2017, National Grid ESO's forecasts were either over or under demand in Britain, in breach of an incentivised programme Ofgem had introduced to check these inaccuracies, according to the regulator.

National Grid said it acknowledged Ofgem's decision and agreed to settle the case, while adding that its processes at the time for new demand forecasts were "not fully developed".

Ofgem said the fee from National Grid ESO would be added to the regulator's voluntary redress fund.

($1 = 0.7265 pounds)

(Reporting by Pushkala Aripaka in Bengaluru; Editing by Shounak Dasgupta)