On a fixed towbar maybe but on removable no, if the tow bar fails (which does happen) then the cable is pointless, it’s designed to last a split second and rip the hand brake up, I wouldn’t attach it to the bar for that reason
Practical Caravan: Removable tow bar failure while towing caravan (1/2)
Practical Caravan: Removable tow bar failure while towing caravan (1/2)