I had a boat trailer once with a folding arm at the front to the hitch. It was an American trailer and my research then said no folding hitch arms allowed in the UK. Annoying as it was a very good feature. Being an american trailer it had other issues that also prevented it being useable here. Shame as it was a great trailer. The rules may have changed in the last 15 years though!
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Re the folding front hitch, Brian James used to make a Caterham 7 sized trailer the micro max with a folding tow hitch. it was a straight square section rather than an A frame & stored vertically. I am sure they wouldn't have made it if it wasn't legal. Bed size was 8ft long and 5"7" wide, with the hitch folded it was about 8'6" x 5'7" including the wheels.
if that was big enough I would be looking out for one of those & putting an extra centre rail on it. Capacity was 1025kg
