The MOT specifies a windscreen area within the drivers' immediate line of sight, which is known as 'Zone A'. If any crack or damage occurs in this area, it must be contained within a 10mm diameter. In addition, any combination of minor damage that, in the opinion of the examiner, seriously restricts the drivers' view will fail the MOT. 

In addition to this 'Zone A' area of windscreen, MOT guidelines requires that any chip or crack within the remainder of the area swept by the windscreen wipers must be contained within a diameter of 40mm.

Some windscreen repair companies - National Windscreens or Autoglass, for example - will carry out a free inspection at their depot of your windscreen and advise whether it is likely to pass or fail the MOT.