suitability of car seats to take child seats is an issue with Land Rover. Land Rover state in their literature that only the front passenger seat in a Defender is suitable for any sort of child seat (except boosters).
BTW if you were thinking of using any of the inward facing seats and lap-belts with booster seats for children then you can't now legally anyway. (You can of course still do it on the forward facing middle seat although I can't see how a booster would help safety on a lap belt) See this below taken from the Road Safety section of the Dept for Transport website:
D. My vehicle has sideways-facing seats
There has never been a legal requirement to fit seat belts in sideways-facing seats. The human body bends forward from the waist - it does not bend sideways and the potential for internal and spinal injury is high therefore if a passenger is secured with a seat belt in a sideways-facing seat. For similar reasons, the type-approval standard for child seats and boosters does not include fixing them in a sideways-facing seat.
A child who is required to use child seats/boosters (ie all those under 135 cms in height who are also under 12 years of age) cannot travel in a sideways-facing seat. A child who needs to use a child seats or boosters must use a forward or rearward facing seat only.