Dubber36 - thanks but that is the exact modle I bought from Amazon only to find that the holding clip goes between the existing mirror casing and the glass, and the gap is too tight - if the door mirror is adjusted when this is in place it looks as if it will break.
I used Milenco towing mirrors on my B7 Passat. The gap between the glass and the casing was pretty tight, but if you tilt the glass down to fit the extra mirror, then adjust the glass back up, it will fit. It's bloody tight and sometimes did rub, but there's nothing that will break. If you need to adjust the glass up and it won't go, just ease the casing away a bit and it will go.
In theory, you should only need to fit them and adjust the glass once. It's not like towing mirrors that were on and off all the time.