Most prop. Chia-Chia. If I remember right only one animal was kept when I visited in 1985 and that was also the year Ching-Ching - Londons other Panda at that time - died, leaving Chia-Chia alone at London.
She is on-display, but I don't recall which one she is offhand; there is a sign mentioning her name and origin, so it's easy enough to find out when there.