It should be very easy to retro-fit.
The fixing points are one pair in the middle of the rear seats, one each side under the rear armrest and one in each of the top corners of the rear parcel shelf.
The rear parcel shelf should have to large plastic screw in finishers already in place, just remove those and bolt in the replacement seat belt anchor. Less than an hour to retro-fit I'd say.
Although someone on here found they were missing one side anchorage point !
Mandatory Seat belt fitting in the rear became law in the UK in 1989, if they are fitted they MUST work.
