Now I may be completely wrong here, but I thought the breakaway arrangement was supposed to do just that. i.e. Apply the handbrake on the towed vehicle and then break.
An emergency breakaway cable must be fitted to the parking brake linkage and the other end clipped or fixed round some fixture on the towing vehicle so that, in the event of the trailer becoming detached from the towing vehicle, the cable will apply the parking brake automatically, before snapping itself. It is not recommended to loop the cable round the towball. (But do so if there is no alternative attachment point.) It is a separate offence not to use the breakaway cable provided.
I can see the point of the strops and chains, but I would be worried about the towed load catching me up if this was the case.
I'm interested as I'm a Arrows Trailer owner and have pondered over this. I got stopped last year on the M5 in one of the big round ups they had for illegal vehicles. No comment was made about the lack of a breakaway cable, but it did get me twitching a bit. I didn't fancy my Land Rover and Trailer joining the car park full of untaxed/un-insured vehicles they had already got.
Nige