At the crossroads of Exhibition Road and Cromwell Road SW7, traffic
approaching from three directions is now banned from turning left or
right. This is signified by the green light being a forward arrow. At
other junctions where both turns are banned you would see a vertical
white arrow on a blue background beneath the three traffic lights, but
they have not done that here. The result is that if you arrive at the
junction when the light is red, you may not know that the turns are
banned until the light turns green, and since most people start moving
when the amber comes on, that seems a bit late to me.

There are currently large banned left and right turn signs on metal
easels, but these are obviously temporary and seem to be an admission
that TPTB know that the lack of the permanent signs is confusing. I am
doubtful that you could be prosecuted for turning when the temporary
signs are gone and the green arrow light is all that remains. The only
other indication that the turns might be banned is that both lanes
approaching the junction have a forward arrow painted on them, but I
know that these have no legal force and can also be found at junctions
where the right turn is only banned part time. So, is the new signage
legal? it seems like a backward step to me.