Britain's National Grid issues warning for electricity system tightness on Friday

Migrating starlings fly at dusk past electricity pylons silhouetted by the sunset of a clear autumn evening in the Kent countryside, in Graveney, Britain

LONDON (Reuters) - Britain's National Grid issued an electricity margin notice (EMN) for 4.00-7.00 p.m. (1600-1900 GMT) on Friday, asking generators if they can make more power available.

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)