Spare energy capacity 'getting tight'
28 June 2013 Last updated at 12:34 BST
The government has dismissed a proposal that big shops and factories could be paid to cut their energy use to prevent shortages leading to blackouts.
The National Grid has suggested large consumers could be asked to lower use between 16:00 and 20:00 on weekdays in the winter.
However, the Energy Minister Michael Fallon insisted the lights would stay on.
Imperial College energy analyst Malcolm Grimston says that there is not a lot of spare energy capacity in the system and this could lead to problems.