I doesn't matter for private use.
You can fit as many seats in the back that you can get insurance for.
hen you get to the MOT station the reg number will tell them what they are testing, in your case a van, so they will not and more importantly have no right to go in the back. If is, I am assuming yours is classed as a panel van, then they do not go into the 'cargo' area, full stop.
Just get your insurance sorted though, for the sake of your own passengers. Also worth bearing in mind that if you have a non fault accident and you are running seats in the back and not told them you will be flucked. Just let your insurance know as a 'mod' and stay under 8 seats inc driver (some companies do 9). Also fit the seats with belts, legally you only need belts on front facers, but you can get custom seats with built in inertia's, search on Ebay, loads safer.
Best of luck, but whoa betide the man that don't be upfront with the insurance, they bite harder than a tiger shark.
Mark, waiting for the surf to get less mushy
