Some interesting information in this thread. Had no idea that having a trailer come away was anything other than a super rare occurrence. I always refer to the USA made towbar setup on my truck as "the full hillbilly" it's mostly made of 1/4" and 3/8" plate, I had to use a couple of jacks to lift it up into position after blasting and repainting it. I occasionally tow a loaded car transporter trailer on this setup, The jacking up the rear on the jockey wheel hitch test sounds like a good idea.
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It is quite likely that that vehicle is not even allowed to tow in the UK at all.
Lots of imports never had the paperwork filled in re GTW so are actually not allowed to tow.
Check your weight plate for MAM & GTW numbers.