rear seatbelts

Haven't seen any mention of this ,so here goes.  Middle seatbelt on rear seat( one that goes inside rear seat back) has developed a problem in that it won't reel out, but stays stiff. Any simple cures ? It's a Pita, as although it's needed forMOT, we seldom if ever carry rear passengers ( other than the dog, which used one of the outers( usually the one behind me so Swimbo can see her). I'm wondering if there's any way I can remove it ( other thas take out back seat), leaving the two other belts in place .