The risk of blackouts this winter has increased compared with a year ago according to National Grid.
It says the closure of some power stations would have left spare capacity on the system at just 1.2%, the worst for a decade.
It has secured extra supplies by paying tens of millions of pounds to have several plants on standby and by asking some industries to switch off power.
The move means overall spare capacity is now expected to be around 5%.
"It's clear that electricity margins for that coldest, darkest half hour of winter are currently tighter than they have been, due to power stations closures", says Cordi O'Hara, National Grid's Director of Market Operations.
To ensure the lights stay on, for the second year running, National Grid will pay firms like Centrica and SSE to keep power plants in reserve.
It is also paying large energy users, such as Tata Steel, to switch off.
A total of 2.56GW of power has been secured which National Grid says will increase overall margins to 5.1%.
That is still lower that spare capacity available last winter after similar measures.
The move will cost £36m and will add 50 pence to the typical household energy bill.