The OS is in a similar position to the Met Office in that it provides a service to Government that has profound defence implications. This is not true of other 'privatised' services such as electricity and water. 

 :The risks, and possible consequences in a worst case scenario, of getting the decision wrong, are probably not the sort that any sane UK government is (or would be) willing to consider. They are the sort of things that give politicians and senior civil servants nightmares.