Why Britain chose Spearfish over Mark 48

Why did the Royal Navy choose Spearfish instead of the Mark 48?

Britain developed Spearfish itself and valued its higher speed relative to the Mark 48.

Britain developed Spearfish domestically and valued its speed relative to the American Mark 48. Domestic control and weapon performance point toward the same procurement choice. This concise comparison does not provide a broader service-history assessment of either torpedo.