I'M SITTING down to write this on September 11. It's a date carved into our consciousness.

Around the world, folk are talking and writing about a day which changed history.

People of our generation often tell me they remember exactly where they were when the Twin Towers were struck, just as our parents' generation never forgot how they learned of President Kennedy's assassination.

On the day, I was in a BBC Television studio presenting live network news. There was a mixed bag of stories: an American hurricane, Palestinian-Israeli disputes over peace talks, and the attempted murder of an opposition leader by Afghanistan's Taliban government.

And then suddenly, there was mayhem. A screen across the studio had the wobbly, but unmistakable image of the Twin Towers on it.

"Tell the viewers what they're seeing" shouted the programme editor. My microphone was live. I began to talk.

We now know so much detail about the outrage, it's hard to remember how little we knew in those first few minutes.

Eyewitnesses were contradicting one another. Word was going round that it was a light aircraft.

"What's happening?" the director screamed in the gallery. No one knew. Were we witnessing an attack on an iconic landmark or a tragic accident? I posed the question on air. But with no answer to give.

TV stations are lonely places. Whilst dramatic pauses are OK, silence is not an option. I had to talk and keep on talking. And get the tone right.

I'd been at university in Boston, and had worked as a speech writer for New York's senior senator Daniel Patrick Moynihan.

I'd lived there for long stretches, and followed American news closely. I was glad I did.

My job was to provide live commentary, and it was on a city and society I knew well.

The BBC switched us over to BBC1, interrupting regular programmes as they do for only the gravest events.

At 14.04, a second plane crashed, this time into the South Tower. It was United Airlines 175 from Boston. The gallery gave a collective gasp before falling silent for a moment.

I heard my voice say "a second plane has hit the World Trade Centre in Manhattan. You are watching live pictures."

That night, off air and at home, I sat up late – like viewers across the world – gripped by the unfolding events and deeply moved by what I'd seen and broadcast.

My time on air had felt dreamlike, with hours passing in an instant, and yet individual moments seeming to linger endlessly.

And now, nearly two decades on, people sometimes ask me what I remember most about the day and it's always the same image which recurs. It's the people jumping.