'Calamity Clare' is accused of sabotage as she fires another furious broadside at Tony Blair

When Clare Short arrived at the BBC's Millbank studio in Westminster yesterday morning, she knew she was about to drop a bombshell. Her explosive allegation that Britain spied on the United Nations Secretary General Kofi Annan may have sounded unplanned and certainly took John Humphrys, the presenter of Radio 4's Today programme, by surprise.

But for the former International Development Secretary, the time had come to speak out after the collapse of the case against the GCHQ whistleblower Katherine Gun, who leaked the fact that the United States had asked Britain to mount a "dirty tricks" operation against members of the UN Security Council in the build up to the Iraq war.

As a member of Tony Blair's war cabinet, Ms Short had been troubled to see transcripts of Mr Annan's telephone conversations. She had been tempted to tip him off at the time, but resisted. Her failure to do so has worried her ever since.

"It troubled me and I decided to bring it into the public domain and that's what I've done," she said. "This is the journey of my conscience. I don't mean it's a perfect journey."

After lighting the fuse, Ms Short left to address a London conference - appropriately enough, on international law. By lunchtime, she was under siege by the media asking her to amplify her remarks to the BBC.

She planned her next moves with her aides in her House of Commons office, deciding to reject demands from government loyalists for a "period of silence" and agreeing to interviews with Channel 4 and the BBC's Newsnight programme.

Channel 4's Jon Snow asked: "You've had many noisy days but few noisier than this. Where do you think it's going to end for you?" She replied: "I'm not troubled about myself. I've reached an age and stage where I'm free to tell the truth and be responsible to my conscience."

There was a rich irony in the timing of the latest and biggest bombshell of Ms Short's career. It ensured that Tony Blair's long-planned announcement of an international commission on Africa at his monthly press conference was completely overshadowed.

Despite her differences with Mr Blair, and her repeated calls for him to stand down, her friends insisted she would not have wanted to eclipse the plan for Africa. Yet some ministers were so incensed at her intervention that they accused her of sabotage. Mr Blair described her actions as "entirely consistent" as well as "totally irresponsible".

In the Blair inner circle, Ms Short became known as "Calamity Clare" as she twisted and turned in the build up to what she regarded as an unstoppable, pre-ordained war in Iraq. In a BBC Radio 4 interview, she said the looming war was "reckless" and that she would consider resigning from the cabinet if there was no UN mandate for military action.

Yet she did not resign, even when Robin Cook did. Mr Blair urged her to stay to influence post-war Iraq. But once she decided to stay, she was, in the words of one Blair aide, "a busted flush" and a "prisoner". She even voted for the war.

Some allies deserted her when she did not resign, as she knew they would. She believes that Mr Blair broke his promises to her that the UN would play a significant role in Iraq's future. She admits now she was a "complete failure" when she stayed on, but is glad that she tried.

Mr Blair said yesterday that Ms Short had been a good International Development Secretary, a post she held from 1997 until her eventual resignation in May last year. She went out with all guns blazing, launching a stinging attack on Mr Blair's "presidential" style. She said he was "in danger of destroying his legacy as he becomes increasingly obsessed by his place in history", and called for an "elegant succession" under which he would stand aside for Gordon Brown.

The Prime Minister has always had a tempestuous relationship with Ms Short. Her reaction when he was elected Labour leader in 1994 was: "My God, what have we done?" Ms Short memorably labelled the spin doctors of the New Labour project as "people who live in the dark". Her honest, free-thinking approach to politics often grated with the disciplinary straitjacket imposed on the party by Mr Blair.

After several frontbench jobs in opposition, the natural rebel found life in government much more satisfying as she moulded the Department of International Development into a body which was admired worldwide.

Ms Short forged an important partnership with Mr Brown, who is deeply interested in third world issues such as debt relief. According to some Labour MPs, she even flirted with the idea of becoming deputy Labour leader and Foreign Secretary in a Brown government.

Significantly, allies of the Chancellor have distanced themselves from her since her resignation and it is unclear whether Ms Short, now 58, would be recalled to the cabinet if he succeeds Mr Blair.

SHORT'S 'TODAY' PROGRAMME CLAIMS

On BBC Radio 4's 'Today' programme yesterday, the presenter John Humphrys was questioning Clare Short over GCHQ...

Humphrys: Diplomatic pressure is one thing, but spying on the UN?

Short: Well indeed, but these things are done and in the case of Kofi's office it's been done for some time.

Humphrys: Have British agencies been involved in spying activities against Mr Annan?

Short: Well, I know. I have seen transcripts of Kofi Annan's conversations. In fact, I have had conversations with Kofi in the run-up to war, thinking, 'Oh dear. There will be a transcript of this and people will see what he and I are saying.'

Humphrys: In other words, British spies - let's be very clear about this in case I am misunderstanding you - British spies have been instructed to carry out operations within the UN on people like Kofi Annan?

Short: Yes, absolutely.

Humphrys: Did you know about this while you were in Government?

Short: Absolutely, I read some of the transcripts of the accounts of his conversations.

Humphrys: Do you believe such operations were legal?

Short: I don't know, I presume so. It's odd, but I don't know about the legalities.