By Nick Assinder
Political correspondent, BBC News website
The Iraq war remains controversial
This is the document many politicians and critics of the Iraq war have been urging Tony Blair to release for two years.
Now it is out it has undoubtedly intensified the pressure on the prime minister over the precise processes which led to his unqualified declaration that the war was legal and, ultimately, the decision to launch that conflict.
However, as the cries of vindication echoing from both sides suggest, it has failed to give the absolute clarity many had hoped for.
The leaked advice shows that on 7 March 2003 the Attorney General, Lord Goldsmith, had indeed set out, in classic lawyers' fashion, both sides of the case for and against the legality of war.
At the end of his opinion there is no firm conclusion that he believed war would have been illegal.
He does, however, state that if there was no second UN resolution authorising war "we would need to consider urgently at that stage the strength of our legal case in the light of circumstances at the time".
Significant question marks
What the leak does show then is that, firstly, Lord Goldsmith did originally raise significant question marks over the possible legality of the war.
Secondly, it showed he did indeed harden up his advice in the succeeding ten days to eventually declare war would be legal.
And that raises the question of how and why he apparently changed tack.
And lastly, the leak raises the inevitable questions over whether MPs and even cabinet ministers who apparently never saw this opinion would have supported the conflict had they seen it.
The allegation has always been that, once it became clear Tony Blair and George W Bush were not going to get the second UN resolution then the prime minister leant on his Attorney General to get him to harden up his advice.
That has always been vigorously denied by all parties, with Lord Goldsmith insisting he had never been placed under any pressure but came to his final opinion entirely independently.
No smoking gun
The fact that both sides in this long-running and increasingly acrimonious row claim the document supports their case is the clearest example of just how it falls short of providing the smoking gun many have been hunting.
But it massively intensifies the pressure on the prime minister to finally, officially publish the full opinion and, more dangerously, allow some sort of cross examination if not inquiry into it.
The opposition parties have lost no time in demanding a full explanation from the prime minister.
And, coming in the closing days of the general election campaign which has seen the prime minister's honesty put top of the agenda, this can only serve to heighten fears that the whole Iraq war issue will blow Labour's campaign off course.
No matter how fiercely Mr Blair defends himself, or he and his ministers claim the leak backs their case, this issue is not now going to go away.
As statements from Michael Howard and the Lib Dems Sir Menzies Campbell have clearly shown, this is set to dominate the campaign - probably right until polling day.