Do buses in London stop on request - require flag down or wave ?

Do public transport buses in London stop on every bus stop automatically or do they stop on request ? Do I need to flag them down ?

If you are at the "Request" bus stop or if you are waiting for a "Request" bus, then you should flag down a bus.

But even if you are at the regular bus stop (not a Request bus stop), you can flag down a bus, just to make sure it will stop.