Christopher Andrew has just published an official history of MI5. Professor Andrew has a vast reputation amongst those who know about intelligence history in the UK. However his book has been criticised. As Richard Norton Taylor argues in the Guardian, Professor Andrew had access to a large amount of MI5 material but his history is no doubt skewed both because he cannot tell us what he had access to and because he cannot tell us what he was denied access to. I'd expect almost everyone reading this to have an instant reaction to that sentence: there are two very justifiable opposite feelings, the first is that if you do not know what a history is based upon and cannot follow from text to source, and if the historian cannot tell you about his sources, then you might as well not trust him- he is an establishment stooge. The second is that MI5 cannot release to the general public operational details from the last ten or fifteen or even thirty years without possibly endangering lives. I do not think those questions are easily resolved: the tension is both constant and difficult and one of the reasons that I do not specialise in that type of history is because the moral dilemma facing the historian is so clear. I do not know if Professor Andrew's answer is good enough- I do know that the question is not easy.