National Grid has slashed its forecasts for the number of big new power plants expected to be built in coming years, while admitting its estimates for the growth of solar farms and other small-scale generators were almost 50 times too low.

Just four years ago the company expected up to 33 gigawatts (GW) of new power plant capacity to be connected to its high voltage electricity transmission networks in England and Wales by 2021.

But this forecast has now been cut to 14GW, the company said yesterday, due to delays to new nuclear reactors such as Hinkley Point, a hiatus in investment in new gas-fired power stations and delays to some offshore wind farms.