British cities would be uninhabitable within days and the country is only a few meals from anarchy if the National Grid was taken down in a cyber attack or solar storm, disaster and security experts have warned.

Modern life is so reliant on electricity that a prolonged blackout would quickly lead to a loss of water, fuel, banking, transport and communications that would leave the country “in the Stone Age”.

The warning comes weeks after the Defence Secretary, Gavin Williamson, said Russia had been spying on the UK’s energy infrastructure and could cause “thousands and thousands and thousands” of deaths if it crippled the power supply.