But then she began talking about "the roots of terrorism" and the coding grew more transparent. The threat posed by Bin Laden and followers, she said, "is serious, is growing and will, I believe, be with us for a generation".

There's the crucial word: generation. When you talk about a "generation" you're broadly defining a set of people born around the same time, men and women who share the same broad tastes and influences. Their generation games can last for 10 years or 20. The term can embrace baby boomers and MTV addicts, see generation X turn to generation Y. But it is as long - and as useless - as a piece of string at telling us when a taste for nightmares will end, or how "sustained campaigns" of fear can be brought to a close.

Does Dame Eliza Manningham-Buller truly believe that the cult of Osama is some passing, youthful fad that will one day be gone, like David Cassidy's fan club? Will it somehow be swept away by new boy bands or iPods? Not exactly, it seems. We must all stand up for our core values, "equality, freedom, justice and tolerance", she says. We must therefore confront "the powerful narrative that weaves together conflicts from across the globe, presenting the west's response to varied and complex issues, from longstanding disputes such as Israel/Palestine and Kashmir to more recent events, as evidence of an across-the-board determination to undermine and humiliate Islam worldwide".

Code-crackers will note that she lists those issues and disputes alphabetically. "Afghanistan, the Balkans, Chechnya, Iraq, Israel/Palestine, Kashmir and Lebanon are regularly cited by those who advocate terrorist violence as illustrating what they allege is western hostility to Islam." They should also note that she goes way back before 9/11, which means before Baghdad and Kabul, too - to the 1990s, when al-Qaida was blowing up Nairobi and Dar es Salaam and killing hundreds of innocent Africans. So these "roots" go very deep.

And where, in any meaningful sense, can they be reckoned to start? Not in Kashmir, against a Hindu enemy; nor in Chechnya, unless Putin has become an honorary pillar of "the west". Did Washington dismember Yugoslavia? Is Tony Blair about to sabotage the birth of a Muslim Kosovo? No, the loose threads of this tapestry lead inescapably back to what she calls "Israel and Palestine". Maybe bringing peace to the Middle East after over half a century of vicious strife wouldn't bring total generation shift, the lessening of a fury, the erasure of hatred. But it would be a beginning, a symbol, a chance to start afresh.

Dame Eliza, essentially, is talking solutions with a grim fervour and logic - for how else, another 10 or 20 years on, do we suppose that succeeding generations in Bradford, Barnsley or Slough will begin to think afresh? MI5 and Scotland Yard can't do it with knocks on the door. Deportations and bans on turbulent priests won't do it, either.

There is some fresh thinking around, to be sure. "The source of the conflict here is not territory, not occupation, not settlers. It is a clash between two people and two religions. Anywhere in the world where there are two peoples and two religions, whether it's in the former Yugoslavia, or the Caucasus, or Northern Ireland, there is conflict."

But these are the malign thoughts of the new power kid on the block, Avigdor Lieberman, deputy prime minister of Israel and passionate advocate of ethnically cleansing his adopted land. Meanwhile, dozens more Palestinians die while the enfeebled government that needs Lieberman inside the tent shells Gaza day after day. Whoops! Nineteen more women and children killed by accident. So sorry ... Let's talk equality, freedom, justice and tolerance.

We pretend that withdrawing from Afghanistan or Iraq will do the hearts-and-minds trick. We pretend (with America's triumphant Democrats as the worst offenders, alas) that Israel can somehow be set to one side while the al-Qaida terror debate rages. We kid ourselves that a Middle East solution - permanent, guaranteed and enforced - is separate and optional. It isn't.

"None of this can be tackled by my service alone," says Dame Eliza. Others "must tackle the causes". And - coded or not - we damn well know where those causes lie.

p.preston@theguardian.com