When did an MOT inspector last look inside your boot? I don`t recall it ever happening in my 20 years of car ownership! Even if it ran under the car, I doubt there is anything specifically in the regs covering that. Beyond condition & fit, I don`t think the MOT tester is interested, to the point where cars not originally manufactured with rear seatbelts, foglights, indicators etc. are not required to install them...but I`ll ask a mate who is an MOT tester later.
p.s. I too have been hit hard from behind, by a skip lorry. I was stopped at a roundabout & the lorrydriver was leaning out of the window cheering & waving at Swindon Town FC passing in an open-topped double decker bus when they went up to the first division. Crunch!!! His front bumper stopped about a foot from the back of my head!