THERE are two chief motivations for publishing a political diary: to establish an historical record of events in the public domain, or to make pots of money.

Alastair Campbell's diary was bound to be the subject of significant public interest because of his position at the heart of Tony Blair's government.

He was brought in to advise the first Labour administration for nearly two decades on how to manage the traditionally pro-Tory media. The fact that Mr Blair now concedes that too much emphasis was placed on media management - or spin as it is commonly known - openly questions Mr Campbell's effectiveness.

Nevertheless, he was in the thick of it during a decade in which a great deal happened: the death of Princess Diana, the Mandelson resignations, the war in Iraq, the David Kelly affair, cash for honours and much, much more.

He therefore has a great story to tell - an important historical record to place in the public domain.

But while his diary no doubt gives an interesting insight into the life and times of a government - including an encounter with Mo Mowlam in the bath - there is a glaring omission.

Mr Campbell has confirmed that he left out big chunks about the relationship between Mr Blair and Gordon Brown to avoid giving Tory leader David Cameron ammunition.

That, in itself, confirms that the relationship was every bit as bad as speculation suggests. And it means that Mr Campbell's diary has such a huge hole at its core that it can hardly be considered as an important historical record.

So why has he bothered? That brings us to the second chief motivation for publishing a political diary.