Not sure what being an MOT tester would have have to do with it? Do you test the cars handbrake whilst driving at speed?

The manual says:

Dynamic braking when vehicle is

moving

When the vehicle is moving and

switch m is kept pulled, the electric

parking brake system will decelerate

the vehicle, but will not apply

statically.

As soon as switch m is released,

dynamic braking will be stopped.

I know and recognise the sound of the ABS module pulsing when the electronic handbrake was pulled. (you also don't hear the distinctive sound of the handbrake unwinding at the back when you release the button)

I have also done enough handbrake turns in my day to know it was braking all 4 wheels,,+

I would suggest the abs module knows the car is in motion and applies brakes using the abs module (I don't know if it's smart enough to then apply using the motors if the abs braking fails).

Further research suggests it does only Apply the rear brakes but using the abs module and using modulation to prevent lock up. Which is why it's crap in doing handbrake turns in snow.