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That's because if you thought that once an electricity generator - whether it be a wind farm or a gas-powered plant - was connected to the national grid it could seamlessly send its electricity wherever it was needed in the country, you'd be wrong.

The National Grid, which owns the pylons, substations and cables that move electricity around the country, is already rolling out a huge investment programme – some £60bn over the next five years - to upgrade the system ready for the new world of clean power.

Mr Parton warns against allowing China access to the national grid: "It wouldn't be difficult in a time of high tension to say, 'by the way, we can turn off all your wind farms'".

It found that Heathrow had "assessed its high voltage electricity supply as resilient due to it having three separate intakes from the National Grid, all with multiple connections to the airport and multiple transformers at the National Grid/SSEN substations providing redundancy in the event of failure".

Ofgem is due to conclude a review of the costs to developers of having access to the national grid.