Did the Royal Navy need 30 to 40 Town-class cruisers rather than the number it built?
Short answerNo; that estimate ignores existing ships and the follow-on cruiser program, so the actual requirement was lower than a blank-slate global total.
NotesThirty or forty ships might be justified if the class had to cover every mission by itself. Britain did not begin from that blank slate: numerous older cruisers and station ships remained in service around the world. The Royal Navy therefore needed the Towns to restore and modernize coverage, not replace every existing hull at once. Follow-on C-, D-, and E-class construction continued the cruiser program after the Town-class batches, further reducing the case for a much larger single class.