The grid operator said there is a system margin shortfall of 1157 megawatts compared with the amount it would like to be available.

"We would like a greater safety cushion (margin) between power demand and available supply," National Grid Electricity Control Centre said in a market update late in Thursday.

"It does not signal that blackouts are imminent or that there is not enough generation to meet current demand."

(Reporting By Susanna Twidale; editing by John Stonestreet)