At the end of the 19th century, Nikola Tesla established the principles of three-phase high-voltage electric power distribution while he was working for Westinghouse in the United States.

In 1925, the British government asked Lord Weir, a Glaswegian industrialist, to solve the problem of Britain's inefficient and fragmented electricity supply industry.

[5] The 1926 Act created the Central Electricity Board, which set up the UK's first synchronised, nationwide AC grid, running at 132 kV, 50 Hz.

The first "grid tower" was erected near Edinburgh on 14 July 1928,[7] and work was completed in September 1933, ahead of schedule and on budget.

This rapid growth led the Central Electricity Generating Board (created in 1958) to carry out a study in 1960 of future transmission needs.

[11] Considered in the study, together with the increased demand, was the effect on the transmission system of the rapid advances in generator design resulting in projected power stations of 2,000–3,000 MW installed capacity.

However, in addition to the technical problem of high fault levels, many more lines would have been required to obtain the estimated transfers at 275 kV.

From 1965, the grid was partly upgraded to 400 kV, beginning with a 150-mile (240 km) line from Sundon to West Burton, to become the Supergrid.

In 2021 a new non-lattice design of electricity pylon, the T-pylon, was built near East Huntspill, Somerset for the new 35 mile Hinkley Point C to Avonmouth connection.

[15] In 2024, the Department for Energy Security and Net Zero established the publicly owned NESO to acquire the electricity system operator license from National Grid plc.

[41] Because of the power loss associated with this north to south flow, the effectiveness and efficiency of new generation capacity is significantly affected by its location.

[48] The UK grid has access to large pumped storage systems, notably Dinorwig Power Station which can provide 1.7 GW for 5–6 hours, and the smaller Cruachan and Ffestiniog.

[51] National Grid is responsible for contracting short term generating provision to cover demand prediction errors and sudden failures at power stations.

[52] Reserve services are a group of services each acting within different response times:[53] These reserves are sized according to three factors:[54] The English and Welsh parts of the National Grid are controlled from the National Grid Control Centre which is located in St Catherine's Lodge, Sindlesham, Wokingham in Berkshire.

Triad dates in recent years were: This is the main source of income which National Grid uses to cover its costs for high-voltage long-distance transmission (lower voltage distribution is charged separately).

The grid also charges an annual fee to cover the cost of generators, distribution networks and large industrial users connecting.

Triad charges encourage users to cut load at peak periods; this is often achieved by using diesel generators.

Due to the nature of electricity demand in the UK, the three Triad periods always fall in the early evening, and must be separated by at least ten clear working days.

The TNUoS charges for a HH customer are simply their average demand during the triad periods multiplied by the tariff for their zone.

[73] In 2020–21, issues affecting the low voltage distribution networks – for which National Grid is not responsible – caused almost all the 60 minutes or so per year, on average, of unplanned domestic power cuts.

While switching the presumed faulty equipment out, an incorrectly sized protection relay installed several years prior caused a circuit breaker to trip, resulting in the loss of supply to two major south London substations.

A week after the London blackout, on 5 September 2003, an incident occurred at Hams Hall substation which affected supply to 201,000 customers in east Birmingham.

Affected customers included Network Rail, Birmingham International Airport, and the National Exhibition Centre, with a total of 301 MW of load lost.

This was attributed to an error made by National Grid when commissioning protection systems after upgrading components in the substation that August.

[75] On 27 May 2008 starting at 11:34, two of Britain's largest power stations, Longannet in Fife and Sizewell B in Suffolk, disconnected from the grid ("tripped") within minutes of each other.

[81] The grid frequency fell to 48.8 Hz before automatic load-shedding disconnected 5% of the local distribution networks (1.1 million customers) for 15 to 20 minutes; this action stabilised the remaining 95% of the system and prevented a wider blackout.

[82][81] Although power was maintained at all times to the railway network (but not to the signalling system), the reduction in frequency caused 60 Thameslink Class 700 and 717 trains to fail.

It found that Little Barford and Hornsea One had failed to remain connected to the grid following the lightning strike, and their operators – RWE and Ørsted respectively – agreed to each pay £4.5 million to Ofgem's redress fund.

[83][84] On 4 November 2015 National Grid issued an emergency notice asking for voluntary power cuts because of "multiple plant breakdowns".

No power cuts occurred but wholesale electricity prices rose dramatically, with the grid paying up to £2,500 per megawatt-hour.