= Solution
At fixed electrical output, improving efficiency from $\eta_0$ to $\eta_1$ reduces fuel and associated combustion emissions by $1-\eta_0/\eta_1$. A change from 0.33 to 0.45 saves about 27%. If an illustrative large coal fleet emits 3.6 Gt annually, that is nearly 1 Gt, exceeding a hypothetical 0.5 Gt national total and far exceeding a 0.1 Gt electricity-sector total. Thus the comparison can be true on reasonable scale assumptions. It is not established by the words “state of the art”: fleet sizes, existing efficiencies, feasible retrofit fractions and whether UK electricity or all UK <energy> is meant must be specified. Continued growth and rebound can offset technical savings, and the options are not mutually exclusive.
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