Personally I would far rather have police people with mobile speed camera things than bumps or fixed speed cameras.

Bumps seem to come in two varieties - the ones which are so steep that unless you slow down to 5mph it seems your shock absorbers are going to come flying through the bonnet (a German car manufacturer now sells special "London" shocks since their normal ones don't last very long in our fair metropolis), and the ones (like Honor Oak Road) which are pointless because anything larger than a Reliant Robin can fly over them with no disruption provided they line themselves up correctly (which sometimes means traffic from opposing directions being right in the middle of the road - I don't understand why they are designed this way myself but I am sure there's a method in their madness).

Fixed speed cameras (like the ones on Peckham Rye) often mean that lots of cars travel at 45/50mph until they get to the camera zone, then they slam on their brakes, slow down to 25mph for about 50 yards and then speed up again. I think this is the pattern of unsafe speed staggering you're talking about above and I really don't think they work when they're on routes which the same people travel frequently and so know where the cameras are and when they can speed, and when they can't.

Never ceases to amaze me when I am driving and travelling at the speed limit how many people feel the need to overtake me.