Hello Gerald,
Just a word of caution here.
Food for thought, based on my opinions.
Firstly, I doubt any bench seat will have Type Approval. You may not care, but your Insurers almost certainly will !
Regarding no seat belts. Almost certainly an MOT fail.
The MOT tester isn't interested in whether the seats are used for travelling, or not.
All they care about is that 'correct' seatbelts are fitted and fully functional.
Your current seats should have lap belts, the minimum requirement for rear facing seats.
Your bench seat, in my opinion, would need them too.
I would check with an official MOT tester before proceeding.