Adding a Trailer hitch to a tipper

My boss wants to add a trailer hitch (>3.5 tonnes) on to the back of a volvo fmx tipper to transport large plant.

Can someone point me in the directions of how you would go about retrofitting the trailer hitch (legally)
TIA

Go to a Vbg agent and get one fitted ,like Euroaxles , vbg at Warrington will tell you the nearest agent for fitting plates ect to you .