This is the BBC.

Just when you think you know where you are,

when you think you know what the news story is,

when you think you know what you've got to get your head round

or that picking cherries and having cake and eating it and pick and mix.

Suddenly another story comes along and looks even bigger than the one you've been focusing on.

I was talking about that to a group of kids in Sheffield.

This podcast comes from Sheffield this week.

And I was recalling to them the time I was talking to Tony Blair's advisor

about what he'd say in a big speech to the TUC

was September 2001.

And just as he was thinking how much to tell me,

his phone went and he looked at me, said, don't worry about it.

You'll never do that broadcast.

A plane has just flown in to one of the twin towers in New York.

For a couple of minutes, we thought that was all it was.

We didn't realise the world was about to change.

Well, it's been a week like that, a week of conspiracy stories.

A week where we don't know when I record this,

who exactly poisoned those people in Salisbury.

But you might by the time you listen to this.

Tonight at 10, Scotland Yard reveals that a nerve agent was used

...