Abandon hope of reading anything remotely original, all ye who enter here. That pre-emptive warning may be implicit in the byline above, but I make it explicit today because what you are about to enter is the tragically unlost Danteian tenth circle of hell that is Mr Tony Blair. If he bores the bejeesus out of this crazily obsessive student of his works, what on earth will another article about him do to those of you in better psychiatric health?

Before you tut, "No, not the bleeding Blair rant, not again," and shift to my friend Mark Steel, a final plea for your attention. There is something scintillatingly fresh to be said of him after all. Mr Tony, the Daily Mail reveals, has become besotted with deep sea fishing. "And we're not talking about him standing about on deck... dangling a rod over the side," a friend is quoted as saying. "Apparently, he gets strapped into one of those high-tech seats with a harness, like in Jaws."

Loss of power is a hateful thing to the average victim of undiagnosed narcissistic personality disorder, so no one will begrudge him the chance to replace the adrenaline rushes as he prefers. The difference of opinion only arises when the scent of rehabilitation brings him home. Just when you thought it was safe to go back in the water, here he is encircling the upper echelons of public life once again - and if his dream of rehabilitation is to be harpooned, we're going to need a bigger boat.

Whether the vessel capable of torpedoing his monomaniacal self-belief is even buildable is another matter. Armed with a cabal of loyalist ultras in the press, shielded by the adoration of a Prime Minister and Chancellor who know him as "the master", perhaps no force on earth can penetrate his titanium shell. Any hope that this might be achieved by the Chilcot Inquiry – you remember; the latest investigation into how Mr T and his A Team (they love it when a plan falls apart) took Britain into Iraq – receded this week.

The report, on which Sir John began work in 1732, has been postponed. This is because the Cabinet Secretary Lord O'Donnell, acting on the PM's behalf and in defiance of the Information Commissioner's order, refuses to release details of pre-invasion chats between Mr Blair and President Bush. Now due late next year, the report has been postponed so often that it reminds me of the ancient Passover tradition whereby we Jews, not one of us with the faintest intent of settling there, mutter, "Next year in Jerusalem".

If Mr Tony were content to remain in Jerusalem next year and ever after, using his status as the Quartet's peace envoy as the launch pad for his charitable and commercial endeavours in the region and beyond, all would be well. Who doubts the purity of his motives in consulting for mineral-rich African countries and oil- and gas-laden central Asian dictators? Who resents him his colossal earning power in countries far away of which we know more than perhaps he would wish?

But he isn't content with that, so back home in Blighty a myth takes shape. This holds that he is a prophet wrongly dishonoured in his own land, that he was kicked out too soon, and that he has much to offer us yet. One understands how the fantasy might gain traction. People forget quickly, and five years after he left, they may associate him with the easy credit boom he oversaw, which allowed them to nip off to Prague for the weekend whenever the fancy took. And as he likes to remind us, he was the greatest election champion in Labour history.

Yet there is only ever one reason why a healthy PM is ousted. It is because he, or she, has become a massive liability. Mrs Thatcher thought herself the victim of treachery with a smile on its face, but she went because a vast chunk of her MPs knew, from the Poll Tax, that she guaranteed electoral doom. Gordon Brown was the instrument of Blair's demise, but the cause was the same: Blair, who only scraped back in 2005 after recalling the sidelined Gordon to co-front the campaign, was poison to Labour's chances by 2007.

He was arsenic in the party's bloodstream for a reason so self-evident that it doesn't much matter what Chilcot concludes. Everyone, or almost everyone, knows it all anyway: that he struck the deal with Bush long before he admits; that it was mendacious drivel to claim Jacques Chirac refused to countenance a second UN resolution "under any circumstances"; that the intelligence was cynically stripped of all caveats for political purposes; and that, in terms of foreign policy catastrophe, Iraq makes Suez seem a trifling diplomatic gaffe on a par with mis-seating the Panamanian ambassador at a banquet.

Call it an atrocious strategic misjudgment, a dementedly misguided Neocon experiment, a war crime or whatever, it is perfectly well understood in these child-like terms: Mr Blair did a truly terrible thing, with unspeakably terrible consequences for the people of Iraq, the troops killed and maimed in prosecuting his folly, and those who died and were injured here in retaliatory bombings in July 2005, the morning after the 30th Olympiad was hereby awarded to the city of London.

It isn't hard to see why Ed Miliband has appointed Mr Blair as his counsellor on the "Olympic legacy". This is one sea monster you'd want inside the aquatic cage pissing out, and in handing him the satirically paltry role of White Elephant Tsar In Opposition, Little Ed shows what a smart operator he is. In lionising the fallen leader and their wide-eyed admiration for his admitted genius for tactical manoeuvring, meanwhile, David Cameron and George Osborne show that power to them is fundamentally a game... one of multi-dimensional chess, perhaps, but just a game for all that.

In politics, very, very few issues can be reduced to unarguable moral certainties. This is one. Tony Blair is no wrongly dishonoured prophet but a pariah in his own land. He is a pariah because he colluded in an act of abundant wickedness, and untold hundreds of thousands died and millions more suffered monstrously in consequence.

It is crude, unoriginal, and, yes, crushingly dull to flog this long-deceased horse again, and if it has bored you half to death to read, imagine what it's been like to write. But so long as this Kraken of deranged self-righteousness believes he has a future in public life, and so long as powerful people are willing to indulge him, it cannot be reiterated often enough.