Is one ship a plausible size for a British class of comparable battlecruisers?
Short answerProbably not; Britain would likely build more than one, with four or possibly eight being more plausible.
NotesBritish capital-ship planning generally sought a usable class rather than an isolated exemplar. The uncertainty lies between a four- and eight-ship program. A single vessel would not provide the distribution and fleet utility expected from the type.