Downing Street's Director of Communications and Strategy, Alastair Campbell, made the following resignation statement on Friday.
Campbell resigned on a day the Hutton Inquiry was not sitting
Prime Minister Tony Blair's full response is also published below.
My family, friends and close colleagues know that I have been thinking for some time about leaving my position as Director of Communications and Strategy. I had intended to leave last summer, but as the Iraq issue developed, the Prime Minister asked me to stay on to oversee Government communications on Iraq, and I was happy to do so.
We agreed on April 7 of this year, however, that I would definitely leave this summer and I have now given the Prime Minister formal notice of my decision to leave.
I did not think it appropriate to announce this on a day when Lord Hutton was sitting, and I shall of course continue to be available to assist his Inquiry in any way he wishes. I will also be available in the next few weeks to assist the handover to my successor, who will be announced shortly.
It has been an enormous privilege to work so closely, in Opposition and in Government, for someone I believe history will judge as a great transforming leader of the Labour Party, and a great transforming Prime Minister.
For someone whose professional interests have always been politics and the media, there can be no better job than the one I have been doing, and I will always be grateful for the opportunities I have had since the Prime Minister asked me to work for him when he became leader of the Labour Party in 1994.
I look back with pride and satisfaction at the role I have been able to play in helping to modernise the Labour Party, in helping the Party secure two great election victories and, more important, in the help I have given the Prime Minister and other Ministers in making the historic changes the Government has made to our economy, our society, and Britain's role in the world.
Ups and downs
Politics, to me, has always been about having an affirmative agenda for changing your country, and the lives of its people, for the better.
This Government has a lot to be proud of. The Minimum Wage. The New Deal. The attack on child poverty. The constitutional changes that have strengthened the UK. Progress in Northern Ireland. Investment and reform leading to better schools and better hospitals. The leadership Britain has shown overseas. I am honoured to have been part of that process of change.
When I first took the job as Press Secretary in Opposition, I recall Ken Baker saying to me that in the media age you can only do a job like this for four years. I have now worked for the Prime Minister for nine years and I know in myself that it is time to move on and do other things, and let others support the Prime Minister in the next phase of the Government's programme of change.
There are huge upsides in a position like this - the people, events and places that you encounter and experience; the feeling that you are able to make a difference; the knowledge that you are witnessing history in the making.
But there are downsides too and these are mostly borne by your family. The reality is that in some jobs, and this is one of them, there is no such thing as a day off, or a night off, or a holiday without interruption. The pressures are real and intense, but in doing the job you learn to live with them. It is your family that pays a price.
Fiona will be leaving Downing Street at the same time, in a few weeks, and intends to return to freelance journalism. We have three wonderful children and we look forward to spending a lot more time with them.
As to my own future, I do not at this stage want to take on another big job as such, but instead for a while hope to do a variety of different things, for example writing, broadcasting, making speeches about the issues that interest and concern me, and on which I have something to say.
I am keen to write not just about politics but other areas of our national life, such as sport. I also want to get more involved in grassroots sports development.
I also intend to devote more time and effort to the Leukaemia Research Fund, with which I worked very closely, when running the London Marathon earlier this year.
And of course, politics having been a passion of my life, I will maintain a close interest in it and I will continue to help the political causes I believe in any way I can.
Finally, I want to thank colleagues across Government, but especially my own team in Downing Street who have been an enormous source of strength and support through the good times and the bad. Not least thanks to them, and the team spirit we have built, I will leave with far more memories of the good days than the bad.
I also leave knowing that despite the pressures and the strains, I have a friendship with the Prime Minister which will endure and I leave knowing that whatever the crises, the dramas, the things that went wrong as well as the things that went right, he gave me a big job, a big challenge and I strove at all times to do it to the best of my ability, and hopefully made a difference for the better.
The picture of Alastair Campbell painted by parts of the media has always been a caricature.
The Alastair Campbell I know is an immensely able, fearless, loyal servant of the cause he believes in, who was dedicated not only to that cause but to his country.
He is a strong character who can make enemies but those who know him best, like him best. His combination to the Labour Party's modernisation, and electoral success, was enormous.
And his contribution during the wars in Kosovo, Afghanistan and Iraq, in particular, were of great importance to the understanding of Britain's case here and round the world.
In the extraordinarily difficult and wearing world of the modern media, he operated with tremendous skill and dedication. I knew for a long time he wanted to move on and I wish him every success.
He was, is and will remain a good friend.