Failure of the National Electricity Transmission System (NETS)

Impact 5
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risk indicator
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ID 26a
Risk theme Accidents and system failures
Impact & Likelihood
Impact key
5 Catastrophic
4 Significant
3 Moderate
2 Limited
1 Minor
Likelihood key
5 >25%
4 5-25%
3 1-5%
2 0.2-1%
1 <0.2%


The National Electricity Transmission System (NETS) transports electricity across Great Britain. A failure of this system has the potential to severely disrupt all other critical systems, resulting in greater consequences than typical utilities failures. Great Britain has never experienced a nationwide loss of power and the likelihood is low, however similar events have occurred internationally. In 2019, in South America millions were left without power following a failure in the electricity system. Great Britain has one of the most reliable energy systems in the world and maintaining a secure electricity supply is a key priority for the government.


The reasonable worst-case scenario is based on total failure of the NETS, which would cause a nationwide loss of power. All consumers without backup generators would lose their mains electricity supply instantaneously and without warning. A nationwide loss of power would result in secondary impacts across critical utilities networks (including mobile and internet telecommunications, water, sewage, fuel and gas). This would cause significant and widespread disruption to public services provisions, businesses and households, as well as loss of life. Reasons for failure could include an extreme weather event, a cyber attack and cascading technical failures.

Key assumptions

For the purposes of the reasonable worst-case scenario it is assumed that the event occurs in winter when there is a high demand for electricity.

Response capability requirements

There would need to be preparations in place to support wider recovery and the continued operation of multiple sectors. This includes functioning telecoms, emergency services and fuel distribution. It would be vital to ensure that fuel is available to priority users and can be distributed quickly across the country as required. To support the immediate aftermath of the incident, resilient communications systems, humanitarian assistance and victim support should be in place.


Within a few hours, small pockets of consumers would be gradually reconnected with intermittent power supply, with a significant proportion of demand being reconnected within a few days to create a stable ‘skeletal network’. Full restoration could take up to 7 days, however, depending on the cause of failure and damage, restoration of critical services may take several months. As the electricity network is often more complex in urban regions, it is likely that rural areas will receive power more quickly. Due to the geographical distribution of generation across Great Britain, northern regions may receive power more quickly.