MGBGT wrote:
Not sure about this, but I seem to remember that any crack in a screen not obscuring the drivers field of vision, if it over 10 cm long, requires the screen to be replaced straight away, and driving on could lead to a penalty for driving a vehicle in an unroadworthy condition; ergo, pull over and ring Highway Windscreens et al...
I'm not sure about this one either - and several broken windscreen have been my only insurance claims in decades. However IIRC there are three zones. Zone A is usually marked out on the windscreen and is roughly a foot-wide band down the swept area in the driver's line of sight. Any damage greater than (IIRC) 10mm in that area is an MOT failure, and so presumably it will be unlawful to drive with more damage in that area than that. Zone B is the swept area not in zone A. IIRC, you are allowed damage of about two inches there. Anything outside the swept area is not an MOT failure and so, presumably, allowed under law.
IG said the crack was not in his line of sight, so I assume not in zone A. So, if the crack was smaller than 2" or outside the swept area, I suspect IG would have carried on, but I'm not sure whether he'd have stopped on the hard shoulder and phoned for a new windscreen if the damage was "more serious" or left the motorway at the next opportunity and driven to a repairer. Pragmatically, I would do the latter (unless the damage seriously impaired visibility) because it's safer to drive a few miles with a cracked screen than it is to wait on the hard shoulder.