"The OGC refuses to publish Gateway Reviews on the grounds that their disclosure would discourage their contributors from making truthful submissions to the process."

Feel free to speculate, but I can't imagine what kind of "truthful submission" you could make to the government, regarding ID cards, which could possible be discouraged by the probability of it being made public. (And I speak as one who has made such submissions)

Only politically revealing (of their true motives) or illegal comments could fall into such a category. All the more reason why we should be entitled to see them.