Generally as a rule of thumb is a trailer is unbraked up to around 750kg and then will be braked over this
I can try and dig out some material from somewhere but the trailers that have handbrakes on them are braked as the hand brake acts as an overide to the braking system when stationary. When moving and the car slows down the weight of the trailer pushes on the drawbar and activates the brakes on the trailer. When reversing there is generally some way of overriding the brake activation by means of a metal flap (thats how it is on the HB505 I have)
Hope this helps! (Sorry if I've not helped you win your arguement!)
They are braked, it is often recommended that when parked, unhitched, the hand brake is not left on as the brakes can stick on if left for some time, if there were no brakes this would not be a problem.
Try putting the argument this way: An Ifor 505 weighs 900 kgs. A 14hh pony (like mine) weighs around 400 to 450 kgs, lets add another, just for fun at 400kgs.
So, now you have a 900kg trailer with a further 850kgs of dobbins =1750kgs. Do you REALLY want to try and slow that lot, coming down the Cheddar Gorge, or Burrington Coombe just using the brakes on you car, which, let's not forget, holds you, your OH and all you tack, coats, hats etc.
Braked. ANY trailer with a Max Laden Weight of over 750kgs must BY LAW have brakes fitted. The IW has a over-run braking system, which is, in non technical speak, the part that is covered by the springy rubber bit on the hitch! The trailer brakes are applied by the braking action of the tow vehicle, using an over-run system (technical speak!). There is also a break-away cable that is attached to the tow vehicle, in the event of an unscheduled uncoupling.