Why Britain has not converted submarines into SSGNs

Why has the Royal Navy not converted existing submarines or retiring SSBNs into guided-missile submarines?

Pressure-hull alterations make active-boat conversions difficult; Vanguard conversion also faces cost, disputed remaining life, and the strain caused by SSBN maintenance delays.

Converting an in-service submarine can require difficult alterations to its pressure hull. Such work risks damaging a scarce boat's usefulness. For Vanguard-class SSBNs, cost is presented as another obstacle, and the remaining service life is disputed: Alex Clarke thinks a few more years could be obtained, while the contrary assessment he reports says they could not. Maintenance delays have also left the deterrent force operating effectively around three boats for a period, increasing the strain on those available.