According to those ubiquitous commentators, “Labour backbenchers”, it was my book wot done it. Within minutes of David Blunkett’s departure they were reported as saying, that had it not been for the revelations contained in my biography of the Home Secretary, he would still be in office.

As Sir Humphrey would have put it: “spherical round objects”. Mr Blunkett resigned for a specific reason. Sir Alan Budd had discovered an e-mail which showed that his private office had, despite Mr Blunkett’s assertions, been involved in the visa application process for his former lover’s nanny.

Yet when the rumours that the Home Secretary was about to resign started to fly around Westminster on Wednesday, my heart sank. The impact of the unfavourable comments he had made to me about his ministerial colleagues seemed to be more damaging by the day, with stories of Cabinet support draining away and the Parliamentary Labour Party beginning to lose patience. And that, clearly, would have been in large measure because of what he had told me about some of his fellow Cabinet ministers.

I felt sick. It is all very well to say — as is true — that I have merely quoted Mr Blunkett’s freely given, on the record comments. But the thought that their publication in my book might have ended the political career of a man whom I have come to respect and to admire greatly pained me.

When I started work on my book, more than three years ago, I admired David Blunkett as a man but was critical of him politically. I wanted to write his biography for two reasons. The first was political. I wanted to understand how the Home Secretary could be the same man who raised the red flag over Sheffield Town Hall in 1980. His life seemed to be a metaphor for Labour itself: beyond the pale in the 1980s, and yet the dominant political force today.

But even without the politics, I was fascinated by his life. How had he triumphed over the seemingly insuperable barriers of his blindness, his mother’s poverty and the way society treated the blind when he was young? How did he cope as a minister? How was his story possible? The more I have come to understand him, the more I have come to esteem him, as I think anyone who gets to know him and his life would.

When I heard Mr Blunkett’s resignation statement, I felt an emotion of which I am not proud: relief. I was, of course, sad to see him depart. But I did not want to go down as the man who pushed David Blunkett out of office. When he revealed that he was resigning for a specific reason, which had nothing to do with me, I felt a wave of relief.

The critical quotes from my biography certainly made a bad situation worse, but they did not cause that situation, and nor did my book do anything other than reflect accurately what Mr Blunkett had told me in our interviews. If Mr Blunkett had never met Kimberly Quinn his words would still have caused a storm — but he would have ridden it out with relatively little difficulty. Mr Blunkett’s problems arose not from my book or anything he told me, but from his relationship with Mrs Quinn, who since their split has sought to destroy him — and has now succeeded in that aim.

All sorts of bizarre accusations have been levelled at me. Baroness Nicholson of Winterbourne, the Liberal Democrat MEP, told me on air, despite not having seen the book, that I had somehow linked together all the juiciest quotes and effectively stitched up Mr Blunkett. Others have said that I must have hoodwinked him into revealing all. It has also been reported that I published off-the-record comments.

None of these accusations are true. I conducted a series of on-the-record interviews, all of which were tape-recorded. Mr Blunkett knew from the beginning that the book would be published before the next election. Indeed, so careful was I not to lead him into an elephant trap, and so open-mouthed was I at his frankness, that I reminded him as he spoke to me that the tape recorder was on. Am I supposed to have censored the remarks, knowing that they would embarrass him? And they were not pieced together, but part of a coherent whole — an analysis of how colleagues and departments were performing. No one from his office has suggested that I have put a construction on his words which they cannot bear, or been underhand. I asked questions. Mr Blunkett answered them.

One is tempted to think that if Alastair Campbell had still been around, the Prince of Wales and Camilla Parker Bowles would have been dragooned into church and married forthwith, as a diversionary tactic from the daily diet of revelations from my book. There were none, however. Indeed, as a case study in how not to handle a crisis, the behaviour of John Prescott and Hilary Armstrong, the Chief Whip, merits close attention. Both seemed determined to keep the story running and to give me as much free publicity as they could muster.

The Deputy Prime Minister attacked me on radio for “a very large measure of personal financial greed” (by which I assume he meant charging for my book) and thus prompted new stories about the very thing he was trying to attack. And then, bizarrely, the Chief Whip found a previously unrecognised use for the book as a Tory-seeking missile — throwing it at the Tory frontbench in the Commons chamber. I owe them both a free copy.

It is difficult to write of a man whom one admires and respects that he is the author of his own misfortunes, but David Blunkett is just that. No one forced him to tell me what he thought of his colleagues. No one demanded that he begin a relationship with Mrs Quinn. And no one commanded him to make inquiries, however vague, about his lover’s nanny’s visa.