So the Defender 90 comes without isofix mount on the front passenger seat as opposed to all other models Defender. In case anyone is interested I just bought and mounted one. LR dealer would not mount it. Liability issue or something.
Easy job not requiring seat out or anything. Just remove plastic outside cover (the one around the seat controls) that's clipped in place and with one screw. Then unhook the seat bottom back fabric with two hooks underneath seat. Lift up fabric and just slide the isofix bracket in place aligning with existing screw holes and fasten with four screws. Took 30 minutes.

Parts needed are
1pc - LR089419 Isofix bar
4pc - LR048645 Screw

Worth noting is that if you put a rear-facing seat in the front it will be harder to evacuate rear passengers in case of emergency. We will only be using the front isofix when there is no-one in the back.