If an A frame is used for towing in the UK irrespective of weight the brakes on the towed vehicle must be capable of being operated where all its wheels are on the ground. Overrun systems are not permitted. A simple Google search results in several self powered electro systems available in the UK
Gordon This firm http://www.roadmasterinc.com make a range of equipment and their catalogue may give you some idea of the systems available here. The breakaway function is an option with the system I have. Of course, individuals need to check the legislation of the country in which they live. Usual disclaimer about this firm other than as a satisfied customer. Nick