The best way to deal with this is as follows.

If there is any object in the view of the driver in the area of where the windscreen wipers operate on the windscreen then that is not permissable and will fail on a MOT or make the driver liable to prosecution (depending on the police officer)
Exclusions to this rule is if the windscreen has and crack (not chip) then that will be a cause for an MOT failure.

Also just an extra note, you do not require a rear view mirror by law. All the law requires in most cars is an offside mirror (drivers side) plus either a rear view or a near side mirror.
So if you have a cracked nearside mirror, as long as there is a rearview mirror and driver side mirror and the nearside mirror has no glass still in it then you cannot fail an MOT for this.