Quite often Medz, they are doing that for a good and noble reason... I'll explain.
It puts a stop to all those 'chancers' who fly down the outside lane, until the very last second, when they then force their way accross into the left lane.
That causes a real snarl up at the very point where the road works begin. Stop - start for hundreds of cars behind.
By doing the blocking trick, it actually keeps the left lane flowing more smoothly.