Evolving Royal Navy attack submarines by batch

Would a larger postwar Royal Navy build repeated Dreadnought- and Valiant-class SSNs?

Yes, though they might be organized as evolving batches of a common design rather than a succession of sharply distinct classes.

A non-declining British Empire could build repeats of Dreadnought and Valiant, though successive Dreadnought batches would be a more characteristically British pattern. Each batch could absorb improvements while preserving a common design lineage. Wartime S-, T-, U-, V-, and A-class development followed a similar evolutionary process even when the names changed. The practical distinction is between continuous batch improvement and genuinely clean-sheet submarine classes.