I was returning from the police chief superintendents' conference at Warwick University when the calls started to come in. Like other senior cabinet colleagues, I made my way to Downing Street and to Cabinet Office Briefing Room A (Cobra). What strikes me now, ten years on, is the calm, the grasp of the enormity of what had happened, but also the preparedness for what we thought would be an immediate co-ordinated attack on London.
That didn't come, but the planning of further attacks did. Hence the appalling events of 7 July 2005 in London and the attempts in London and Glasgow in 2007. Our security and intelligence services were in the front line of protecting us and still are. It was not days, but weeks after that, on 15 October, that I made a statement to parliament laying out precisely what we felt needed to be done - the legislative changes required and, yes, the proportionality between respecting civil liberties and protecting the life and well-being of the nation.
Parliament responded at its best. Both the Commons and the Lords debated and in some cases amended the draft legislation. Through our free media, the debate raged, as it still does, about how we balance the liberty of the individual with the prevention of the most heinous attacks by those who hold our open society in contempt.
Time gives us pause for thought. It also allows us to reassess how to approach the challenges of the future. But anniversaries give us an opportunity to remember. My life changed on 11 September 2001. Much of the agenda that I'd set out back in June that year as the new home secretary was either dislocated or deferred. But, for tens of millions of people across the world, too, life changed for ever.