Could more British submarines block the French Atlantic ports?

Would concentrating more British submarines off Brest stop German capital ships entering or leaving?

It would add danger, but Germany could concentrate its limited torpedo-boat escorts for a single major movement.

Britain did maintain submarine watches off the French Atlantic ports, although they failed to stop the Channel Dash. Concentrating more boats would increase pressure but would not remove the German escort problem. Germany possessed only a limited number of suitable escorts, yet a one-off capital-ship movement allowed those torpedo boats to be surged together. Operation Berlin itself was delayed by escort availability, showing both the weakness and the temporary concentration Germany could exploit.