I have a 07 Clubman, and they fold by pushing the top half towards the window. It helps if you look at the neck of the mirror there is a horizontal line, that is the fold line, twist there towards the windscreen and it should pivot!
If yours are stiff, I suggest you grab the housing with two hands and twist it to fold the mirror in - If you find it hard with one hand, you may be trying to push it where it doesn't want to go.
As mentioned they do fold, if stiff a lick of WD-40 on the joint will free them up. I recon the stiffness you're feeling is because you're trying to fold them straight back. In fact they fold in a upwards motion. Hold the mirror with two hands cupping up and fold anticlockwise in a upwards motion as if pushing the mirror up to the door window, it should move quite freely, as gbwongy said look at the line at the base. hope this is of help
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