Cause of huge blackout remains unclear as electricity returns to homes - More than 90% of power restored in Spain and Portugal as authorities try to find the cause of outage

Red Electrica, Spain's power operator, says that as of 06:00 local time (05:00 BST), 99.16% of power has been restored to mainland Spain. "All substations on the transmission grid are operational. We continue with the restoration work," the operator says.