Wanting to put in rear seats in a 2007 tdci. What's legal and what's possible?

Would I be correct in thinking that I'm only allowed "legally" to fit the forward facing tumble and fold-up seats in a post 2007 TDCI SW?
I'd quite like a couple of flip down single inwards facing seats at the back or a bench on one side.
Is this possible and is it legal as far as an MOT is concerned?

It would appear that it’s legal, if you really want to do it, but not recommended.