By Andrew Walker
BBC News Profiles Unit
Tony Blair's unprecedented announcement, made last September, that he will leave Downing Street at the end of a third term in office, has already changed the tenor of this election campaign.
Tony Blair: The election will be a stern test of his political record
Today, eight years after sweeping to power, the Prime Minister stands at the threshold of yet another remarkable political achievement.
Should the Labour Party secure a third consecutive election victory, Tony Blair, already the longest-ever serving Labour prime minister, would also be set to
become the first Labour premier to enjoy three successive terms in office.
But, as he well knows, this election will deliver a decisive verdict, not just on the New Labour project, but on Anthony Charles Lynton Blair himself.
The political landscape of Britain has been radically altered since Tony and Cherie Blair were welcomed into Downing Street by a highly-orchestrated crowd of ecstatic Labour activists on the afternoon of Friday, 2 May 1997.
To be sure, the areas on which he focused in the 1997 general election - education, the NHS and crime - still remain at the core of Labour's programme.
Record expenditure increases on health and education have been offset by controversy over waiting lists, dirty hospitals and the introduction of higher education tuition fees.
The economy, run almost as an independent fiefdom by Gordon Brown, is generally felt to be doing reasonably well. Blair himself has become a major figure on the world stage and he remains eager to do the job.
But the September 11 attacks, and the ensuing 'war on terror', have transformed Tony Blair from a politician with a largely domestic agenda into a war leader whose advocacy of the invasion of Iraq has split public opinion and divided his
War leader: September 11 transformed Blair's premiership
The fallout from the Iraqi conflict has been immense.
The row over the exact nature of intelligence claims about Saddam Hussein's regime, 'dodgy' dossiers on Saddam's weapons of mass destruction, weapons which even Blair now admits probably do not exist, and the David Kelly affair, ending in the suicide of the government scientist and a rift between the government and the BBC, have all coloured Tony Blair's second term.
As he said at the 2004 Labour Party conference: "I never anticipated spending time on working out how terrorists trained in a remote part of the Hindu Kush could end up present on British streets threatening our way of life.
"And the irony for me is that I, as a progressive politician, know that despite the opposition of so much of progressive politics to what I've done, the only lasting way to defeat this terrorism is through progressive politics."
Beyond the daily cut-and-thrust of political life, Tony Blair has also been looking to his own political legacy. Provided that the Labour Party wins the election, Blair's greatest wish is for a resounding 'yes' vote in the referendum on the EU constitution, expected to be held in 2006.
A victory at this poll, though currently highly debatable, would set the seal on the Blair premiership and leave a lasting monument to his success.
Will Gordon Brown take over at Number Ten?
A series of recent mild health scares, coupled with his own decision not to seek a fourth term, have led to speculation about Tony Blair's successor, too.
Put simply, the bigger the Labour majority, the greater his room for manoeuvre. Will he anoint Gordon Brown as the next prime minister or bring in one of his own cronies, perhaps Alan Milburn?
Whatever the case, Tony Blair's last electoral hurrah as Labour leader could set the seal on a spectacular career or bring down the curtain on a gifted politician who just flew too close to the sun.