A small SSBN fleet is less of a concern for the UK because their submarines are very good, and the only navy that might have better is one of their strategic al

A small SSBN fleet is less of a concern for the UK because their submarines are very good, and the only navy that might have better is one of their strategic allies. You've got to remember each nuclear power is playing a different game; the strategies they choose are informed by their national strengths and weaknesses and who their allies and adversaries are.