My rough calculations give it 15 stops for 2420m in direction 1 (avg 160m), and 2235m in direction 2 (avg 148m).

Alas, it appears that route 631 has it beat - 1440m in direction 1 (avg 130m), 1751m in direction 2 (avg 134m)

(although, peculiarly, the information in TfL's bus route download doesn't match what you get from the web site when you look up 631.)