Here is the text of today's letter from Tom Watson, junior defence minister, to Prime Minister Tony Blair:
The Labour party has been my life since I was 15 years old.
I have served the party at every conceivable level and your own leadership since 1994 in a dozen different capacities, latterly as MP for West Bromwich East, a government whip, and as parliamentary under-secretary of state at the Ministry of Defence.
My loyalty to you personally, as well as to the party and the values we stand for, has been absolute and unswerving.
The struggle to fashion the kind of credible, convincing, effective Labour party you now lead has been the preoccupation of my adult years.
My pride in what our government has achieved under your leadership is beyond expression.
We have revolutionised the lives and expectations of millions of our citizens, combining social justice with prosperity in a way which is unprecedented in the history of our country.
Your leadership has been visionary and remarkable. The party and the nation owes you an incalculable debt.
So it is with the greatest sadness that I have to say that I no longer believe that your remaining in office is in the interest of either the party or the country.
How and why this situation has arisen no longer matters.
I share the view of the overwhelming majority of the party and the country that the only way the party and the government can renew itself in office is urgently to renew its leadership.
For the sake of the legacy you have long said is the only one that matters - a renewed Labour party re-elected at the next general election - I urge you to reconsider your determination to remain in office.
As you know, I had a conversation with the chief whip last night, in which she asked me to withdraw my support from the 2001 intake's letter calling on you to stand down, or my position would be untenable as a government minister.
I have reflected on this overnight. I cannot withdraw my name, and therefore I accept her judgement.
I do not believe that statements so far give us the clarity necessary to progress over the next year.
Nor do I believe that newspaper reports of potential dates which may have appeared since I signed the 2001 intake's letter can provide the clarity the party and the country so desperately need.
It is with the greatest regret, therefore, that I must leave the government.
Tom Watson MP
West Bromwich East