Why Milford Haven is not a ready-made nuclear submarine base

Could Royal Navy submarines move to Milford Haven if Scotland left the United Kingdom?

Not readily; Milford Haven would need major investment and its energy terminals create difficult access risks, making an existing nuclear-certified port more plausible in the short term.

Milford Haven faced two immediate constraints: extensive investment would be required, and the waterway's oil and gas terminals complicated safe submarine access. Nuclear boats are particularly vulnerable to collision hazards while manoeuvring through confined approaches and changing depth. Faslane avoids some of those problems, while Plymouth offered the more plausible short-term alternative because of existing nuclear certification. A permanent replacement base would still demand a separate long-term site and infrastructure decision.