National Grid Electricity System Operator (ESO) has lowered its forecast for the supply margin over the coming winter to 3.9GW - or 6.6% – following a fire at the UK substation for the IFA interconnector with France last month. The de-rated margin is down from the ESO’s preliminary forecast of 4.3GW – or 7.3% – in its early view in July and from 4.8GW – or 8.3% - in last year’s winter outlook.