I'm afraid I wasn't able to rent a helicopter for these pictures, so this is the best I could manage for the double mini-roundabout junction in Stalham. It's not too clear, but those white circles are slightly raised -- You can drive over them with a slight bump.
Notice in this second picture how the "bump" is way over to the left. In theory, one is supposed to keep to the left of it and drive right around it. In practice, most drivers approaching from this direction just go straight across to the right of the bump if the road's clear:
Finally, it's not very clear from the photo, but there's very little room between this "bump" and the curb behind it in which to turn. Again, theoretically drivers approaching from this direction to turn right are supposed to keep to the left and go behind the circle. In anything but the tiniest of cars, it's almost impossible to do so without at least partially driving over the hump, so almost everybody just drives to the right of the bump (the street to the right is one way anyway, so nothing's approaching from that direction).
Buses, trucks, and anyone hauling a trailer just have to use the whole width of the intersection and drive slowly over the top of the humps.
[This message has been edited by pauluk (edited 03-15-2003).]