I have just watched the video twice from Gaz's viewpoint and I also know that particular junction. Other than the fact from the video that the vehicles near side mirror appeared to have tape holding it together and out of position I couldn't see what the driver had done wrong.
In fact I would go so far as to say that lanes 1+2 at that junction allow you to go straight ahead, lanes 3+4 bear right.
The only person that seemed to be at fault would be the cyclist in front of Gaz and Gaz himself for poor road positioning.
If you have used this junction before Gaz, I am sure that you will have seen numerous vehicles take exactly the same route and if you had witnessed prior to this video that you thought the drivers standard of driving was not up to par, then maybe and if I had have been in your shoes, you should have hung back just to be safe.
And I know it's not much of a consolation but this particular vehicle by it's size is NOT an HGV, it's a 7.5t vehicle which your average bod with a car licence* can drive.
* Drivers who passed their car test prior to 1991.