A quarter of a century ago, the first quarter of 2001, Britain used 39 TWh of coal electrical generation, 36 TWh of gas and 21 TWh of nuclear.

Today we're lot more energy efficient†, and the renewables made more than 25 TWh, but nuclear is now less than 10 TWh, we of course no longer burn coal, which leaves 30 TWh of gas still and we have a lot more imports (because we have a lot more interconnect, which is also a form of energy security)

† For example back then we mostly used incandescent light bulbs! And a lot of people still used CRT televisions back then!