Some interesting responses to my question about “pushing the button”. Thanks to everyone for your input.
There is no need for me to go into further details -, since the button-actioning was the only area of discord amongst me and my pals.
We have now found the User Manual for the car, which makes things quite clear.
To set: Lift the handbrake lever.
To release: Depress the button, lift the lever slightly, then (with button still depressed) gently lower lever to the horizontal.
Phew… 