What should have followed the Upholder-class submarines

Were the Upholder-class boats intended to be the Royal Navy's final conventional submarines, and what would have followed them?

No. Another SSK class was expected to incorporate the next stage of technology, consistent with a British pattern of alternating conventional and nuclear attack-submarine development.

Upholder was not intended as the last Royal Navy conventional submarine class, and some planned boats were never built. The class put technology comparable to contemporary British nuclear boats into an SSK hull. A successor was expected to absorb the next increment of development, making cancellation a break in a continuing design sequence rather than its planned conclusion.