A spokesman said it was "simply not true" to suggest that the Grid was in danger of not being able to meet demand, forcing it either to reduce voltage - which makes lights go dimmer - or impose selective power cuts.
The fears have been fuelled both by worries that gas-fired power stations with interruptible supply contracts could be suddenly taken off-line and by the surge in demand during peak periods which has occurred this winter.
The big test could come on the second Tuesday of the month - 14 January - in theory the day of reckoning when demand traditionally hits its annual peak.
Heavy industrial users of electricity and power station chiefs themselves have been voicing increasing concerns about the ability of the system to cope with demand. In the last year there have been nine so-called "near misses" when the system has come close to collapse.
But the Grid said it was confident that it had enough surplus generating capacity to meet whatever demand the worst cold snap could produce.
"There is more than 60,000 megawatts of capacity linked to the transmission system while peak demand last winter was 48,700 megawatts," the spokesman added. "It is simply not true to say the system is in danger of collapse. The amount of planning that goes into scheduling plant months ahead is huge. There are hundreds of engineers working on this night and day, both at our national control centre and in the power stations."
Part of the Grid's problem is that most of the country's power stations are located in the North while the majority of demand is in the South. This can cause bottlenecks in the Midlands, forcing Grid engineers to call up more expensive generating capacity in the South to meet demand.
It has two methods of meeting unexpected shortages. One is to issue what is known as a Notification of Inadequate System Margin - an invitation to generators to bid more expensive plant into the electricity pool to ensure demand is met.
The second is reserve capacity it keeps on the system to meet sudden surges or unexpected breakdowns forcing power stations to trip out. The standby capacity ranges from 400 megawatts to 1,500 megawatts.
Plant availability during the winter peak has risen from 97.1 per cent at the start of the decade to 98.7 per cent last year. However, plant margin - the amount by which installed capacity exceeds forecast demand - has been steadily falling as older power stations are retired and not replaced at the same rate. Plant margins are running at 20 per cent compared with 30 per cent and higher in the early 1990s.