Child of war has grown into empire-building emblem of France's energy security concerns

It is hard to overestimate the political importance in France of state-controlled nuclear power specialist Electricité de France, or EDF. Forged as an engine of national regeneration after the second world war, it was not until 2005 that just 15% of the enterprise was floated on the Paris stock exchange. The government retains a grip on the remaining 85%.

Despite now being run as a stock market-listed company, EDF remains at the heart of French energy policy, which since the oil shocks of the 1970s has been dominated by concerns about national energy security.

After decades of investment, 78% of French electricity now comes from nuclear power stations. EDF has become Europe's largest electricity generator, supplying 38.5 million customers across the continent, with plants capable of producing more than 128 gigawatts. Its 58 nuclear plants on 19 sites account for 72% of its electricity production.

As other European countries opened their energy markets to competition, EDF expanded aggressively. In the UK, its subsidiary EDF Energy was formed after acquisitions including Seeboard, London Energy and SWEB Energy. It has more than 5 million customers.

EDF was established in April 1946 when communist minister for industrial production Marçel Paul - a former Resistance leader, tortured prisoner of war and Auschwitz survivor - nationalised vast swaths of the electricity production and distribution industry under a state-owned "public undertaking".

Early years were characterised by a country awash with Marshall loans embarking on bold projects to build generators and a transmission network across France. These efforts were exemplified by the Tignes dam, the biggest hydroelectric generator in Europe when commissioned in 1952. EDF buses toured towns and villages encouraging households to wire up and be part of a France of the future.

A wave of cheap and abundant oil imports in the 1960s kept the costs of electricity supply down, allowing demand to grow as more and more household and industrial appliances came with cords and plugs. The breakthrough for EDF was the arrival in 1971 of electric heating.

But in 1973 France's era of easy energy came to an abrupt close as the Opec cartel of oil-producing nations began asserting its control over prices. With about half of its electricity generation from oil-fired power stations, France was hard hit. Thirty years of postwar good fortune - Les Trente Glorieuses, as economists labelled them - were over.

Realising the importance of energy security, France's response was to focus on investment, through EDF, in nuclear generation while increasing tax on petrol and encouraging energy-intensive industries to shift from oil to other fuels. "We don't have oil, but we have ideas," became the slogan of national energy independence. The government committed itself to build 13 nuclear power stations within two years.