1996 Vauxhall Frontera nearly fire in boot from underside

this is my mums car that I am using. I had it MOTd on saturday. When driving home from work (20m) i could smell burning and heat coming from the rear. When I opened the back door the bag of clothes in the back had a hole melted through,clothes were burnt/scorched and boot lining also. the whole boot floor was roasting hot. there is oil on the bottom of the rear diff. Could this be a blown seal? would that explain the immense heat and burnt clothes/bag?? very confused and reluctant to drive to a garage..attached pic of burnt hole in boot.