Hi,
The handbook shows that universal car seats can be fitted in the front passenger seat and both rear seats. One exclusion to this is that Group 0 (birth to 10kg) infant car seats and car cots cannot be installed on the front passenger seat.
There are ISOFIX points in the rear seats, with top tether loops located under the cover behind the top of the backrest on the rear seat.
To answer your specific question though, the handbook just states that when fitting child seats in the rear, move the front seat forward, then put the seat back in the upright position to leave enough space for the child's legs. The front seat can be moved forward further than the intermediate longitudinal position if more room is required.
This would suggest that it is possible to have a child seat installed and for a child to use it without having to fold the seat right down.
As jactac stated, I have also had both my kids sat in the back (daughter 9, and son 12) without any issues, and I am sure the average 12 year old takes up more room than a child seat and infant.....