I suspect that unless your van has actual provision for the fitting of seats, you would fail the MOT by installing your own.
Seat belts, proper fixing etc are all considered as part of the MOT. Your vehicle documents will also state the number of 'seat' (passengers) which would mean extra tests etc
Might be entirely wrong on this but lets see how we go....
thanx for the reply, i was thinking along the lines of sourcing a sudo taxi or like for a donar seat maybe breakers evilbay etc. or is there any specialist firms which do crew van conversions or anyone done this themselves.
cheers