Rigid fold-up bike rack. Nice piece of kit. comes with the third bike adapter and the fitting kit 973-16 (I think - its the one for the mk2 Zafira.
One of the plastic tighten knobs that holds tightens/loosens the ridges that the wheels go in to has fallen of so you now need to use a socket although I think its quite easy to get a replacement and only an issue if you constantly change the position and wheel base size of bikes!
Fitting kits for other makes available from as little as £25 on ebay.
Description of it here: http://www.thuleonline.co.uk/product/177-56/Thule-973-BackPac-Rear-Mounted-Cycle--Bike-Carrier