Well, UK Power Networks, the main electric grid for London and most of South-East England was owned by a Hong Kong company until recently (they sold it to the French). So basically Xi Jinping had the power to unplug the British Government at the snap of a finger.
Being owned by a foreign company is not the same as embedding technology controlled by a foreign intelligence service deep into your infrastructure.
The hypothetical snap of the finger from Beijing to shut down power in London (assuming that local operatives would indeed comply, which is not given) could have been easily reverted in a few hours with a snap of the finger from London to replace key people in the company hierarchy or place the company under public administration.