If a woman had behaved the way he did, she would rightly be called a bunny-boiler

For the love of wee William or the love of David? It is almost impossible to look back at the Home Secretary's behaviour last week and believe he was acting for anyone but himself. Blunkett knows better than anyone that without power, without the privileges of government, a ministerial salary and all the perks, the struggle to regain his political credibility and to fight for access to the "little lad" we heard so much about in his resignation speech, his future is bleak.

The fact that he is blind only heightens the hardship and the heartache he faces. He spoke on the night he resigned of the "months of depression ahead" in a way only a man used to utter darkness could.

Blunkett's blindness is the key to both his greatness and his destruction. Over time, it has both hardened and focused him, made him both great and small, magnanimous and mean. All this has been paraded before us since news of his three-year affair with Kimberly Quinn broke in August. David Blunkett has learnt to live in a parallel universe, and what we have seen in the past week is that he also occupies a parallel moral universe.

No man could have fast-tracked his former lover's nanny's visas, resigned before an official inquiry found him guilty of gross misconduct, and then claim, in the most sanctimonious of manners, that he had "done nothing wrong". Welcome to the parallel moral universe of David Blunkett, where having a three-year affair with another man's wife is not wrong; where fathering one, perhaps two, children with her behind his back is not wrong; where allowing his private office to be used to fiddle a nanny's visas is not wrong.

For all the protestations, he leaves with his integrity in shreds. However much we may feel for the man, he behaved abominably towards Kimberly Quinn, her children and the public. Mrs Quinn was a married woman who had an affair and chose to stay with her husband. Blunkett systematically set about trying to destroy her marriage. If a woman had behaved the way he did, she would rightly be accused of being a bunny-boiler. As Blunkett said when he was still clinging to his job by his fingernails, we all make mistakes, and we do.

Many love where they shouldn't; many bend the rules to accommodate a demanding lover, but it doesn't make it right. If we cannot tell the difference between right and wrong, if we cannot voice that opinion of the behaviour of others, we are lost as a society. And yet that is exactly what we are expected to do over Blunkett.

Blunkett said in his resignation speech: "I believe these issues would not have been raised had I not decided in September that I could not walk away from my youngest son." St David would have us believe he is simply the victim of a vengeful woman. Somehow he feels Kimberly Quinn's appalling behaviour exonerates him from his actions over the visas. It does not. It is his moral blindness kicking in again.

It is true that issues would not have been raised if he and Mrs Quinn had not fallen out in such a spectacular way, but what about the visas? What Blunkett really means is that he wouldn't have been caught, that he would rather Sir Alan Budd was not asking awkward questions about shredded documents, collusion between the Home Office and the immigration office and missing records of key telephone conversations. Yet still he weeps his innocence.

How could the Home Secretary have stood before the nation on Wednesday night crying over his son and say he had done nothing wrong? What sheer misplaced self-righteousness. I suspect the intensity of his private world, the separate universe he has inhabited for a lifetime has made Blunkett so sure of himself in everything, as he is over the righteousness of his cruelly public paternity battle.

But to use your "little lad" as your reason for resigning, instead of your abuse of your ministerial position, to make him responsible for the end of your career is a step too far for any loving father. In that misguided resignation speech, Blunkett put the blame for a ruined career squarely on his son's shoulders. How William will feel when he grows up and discovers that? It is nothing short of emotional child abuse.

These are the acts of a supremely selfish man, a man gone mad with bitterness and disappointment, as bad as the vicious Kimberly Quinn who used, scorned and destroyed him.

Such is the widespread disgust now for Kimberly Quinn, a woman prepared to use every means at her disposal to destroy her former lover that the story doing the rounds is that the chid she is carrying is neither Blunkett's nor Quinn's. Frankly, she has no reputation left to destroy, so comments by her husband when she left hospital on Friday that she felt "put upon" are simply astounding. She has ruthlessly orchestrated the destruction of a man she once loved so much she bore his children.

Neither she nor Blunkett comes out of this mess with any integrity. The only thing that unites them now, apart from a lifetime of miserable contact over their child, is each person's belief in their own self-righteousness. And if Quinn or Blunkett seriously believes either of their behaviour has been right, then they occupy a different moral world from the rest of us.