Why modern Royal Navy patrol ships are lightly armed

Why does the Royal Navy no longer operate heavily armed patrol boats?

Its patrol ships are designed mainly for fishery and constabulary duties, while small armed craft could be built relatively quickly from Britain's existing boatbuilding base if a war required them.

The River-class force is lightly armed because its routine purpose is fishery protection and other constabulary work instead of combat in a high-threat environment. That judgment fits the short and medium term, while long-term needs remain harder to predict. Britain nevertheless retains a vigorous small-boat base through RNLI lifeboats, yachts, and motor launches. Those yards and skills could produce fast attack craft relatively quickly if weapons and engines were available. A future mobilization would also have to decide whether the boats should be crewed or uncrewed instead of simply reproducing a Second World War design.