The Labour Party’s decision to flip the switch on plans to bring energy under state control has sparked outrage in an already embattled market.

The looming risk posed by Jeremy Corbyn’s threat to nationalise the UK’s £60bn energy networks industry has stalked the City for months. It first emerged in 2017, softened by vague political rhetoric and doubts over the party’s chances in a general election.

Since then, the unraveling of political norms in Westminster has sent shivers through the City as the hazy threat of a Labour government came into sharper focus.

Now the party’s blueprint for wresting back control the British energy system's arteries and infrastructure have been laid bare in a leaked nationalisation plan.

The sweeping strategy goes far beyond the City's worst fears.

It takes aim at FTSE 100 energy giant National Grid, as well as the network businesses owned by Big Six energy suppliers SSE and Scottish Power. All 19 of the UK’s regional energy networks, once beloved of major international infrastructure investors, will be brought back under public ownership. The vast control centres, which balance the UK's energy system on a second-by-second basis, will also be handled by the state.

“It’s an absolute reversal of thirty year of energy policy," says one senior City source. "A whole generation of investment has been undertaken on the basis of a system which will now disappear.