Its not a van. Simply a Micra with seats removed. I've temporarily removed front/rear seats many times in all my vehicles to aid carrying strange loads.
Op mentions the dangers of the vehicle in this condition - spare wheel not secured is agreed not a great idea but is hardly any more dangerous then if it still had an interior - rear seats aren't a bulkhead, any heavy item unrestrained will burst into the passenger area in a shunt.
Unless its details have been updated by DVLA its still a 5seat car but with seats removed at present!
Additional. Not all vans have bulkheads or other devices to protect the driver - hijet vans for example.