These diaries are not "The Complete Diaries", they are "The Edited Diaries". The title is highly ambiguous and contradicts itself, and could end up being misleading. With that out of the way, on to the product itself.
These edited diaries could be viewed as accompaniment to the biography by Ion Trewin, who also edited these diaries, which have been selected to trace Clark's rise and demise in the political arena.
Political scholars should instead make sure to buy the complete diaries of the period/s they are interested in. They are in three volumes, the first of which, "In Power", is the most well known, covering Alan Clark's period in government (1983-1992). If you want the steamier side of Clark's life, then once again buy one or more of the original diaries, this is not for you.
If, however, you want an understanding of the man himself, and do not have the time or money to go through three separate volumes, then it is hard to fault these.