You and I know the score....
"1.12 The variety of loads, vehicles and operating conditions make it impossible to cover all the circumstances likely to be encountered by drivers and operators.
This Code must therefore not be regarded as exhaustive or exclusive, but it does apply to all vehicles from the smallest car derived van to the largest goods vehicle. Satisfactory securing methods not mentioned in this code do exist, and others will be developed. However, the basic principles described in this Code must be complied with, irrespective of the actual method used to secure the load."
If you wound up in court it would come down to a question of whether the setup was adequate. Furniss's setup ticks a big box by getting the excavator as close to the headboard as possible. which satisfies the restraint of 100% of the load, so the chains on the blade holding the machine back are bonus points. The front chains would theoretically be only needing to hold 50% of the load, as arguably the sideboards also can do for the sideways forces.
It is all a argument to be had, but i'd happily argue my case in court.
Hookloaders NEED chains from headboard to machine...... otherwise when it goes wrong it goes real wrong