In the UK a trailer that has brakes, whether above or below the 750kg weight limit (at which point brakes become compulsory), must have those brakes in working order. Although the R4 is under 750kg - because it is being towed as a trailer, it's brakes must function.
I think there is possibly an exemption from this when using the recovery type A frame that André is describing, but the fixed type, that would typically need to be used behind a motorhome, certainly have this requirement.
The braking is typically achieved using a cable attached to the car's brake pedal and to the braking type tow hitch. There are electrically operated systems but they are quite expensive.
There are several UK companies that will do this work for you - it is necessary to fabricate special mountings for the a frame.
I have bought a second hand frame for mine (£150) but have yet to tackle the mounting of it.