Dubai: With the British Labour Party beginning to elect a new party leader, the legacy of Tony Blair is casting a long shadow over its future.

“The verdict of history on all prime ministers after they leave office remains hotly disputed, but few in modern times have been subject to as much hostility as Tony Blair,” his biographer, British political historian Sir Anthony Seldon tells the BBC. Blair succeeded to the leadership in July 1994 and set about “modernising” the Labour Party so it embraced rather than rejected capitalism, and sought to rule in the interests of the whole country, not just the working class and trade unions, Seldon notes.

Coming to power after four election defeats for Labour in a row, 1979, 1983, 1987, and 1992, Blair’s formula proved outstandingly successful. He won the general election in May 1997, with a landslide victory against the discredited Conservative government, won again with a landslide in 2001, and won a third time, albeit it with a smaller majority, in 2005. No Labour leader in history ever won three election victories and lost none.

“One would expect the Labour Party to revere Blair as its greatest electoral asset. But the opposite is true,” Seldon says. “He is reviled by many in the party, and his supporters are in decline as a new generation of Labour MPs has entered Parliament, rejecting Blair and the way he tried to rid their party of its left-wing elements.”

Seldon is vice-chancellor of the University of Buckingham. A noted political historian, he has written biographies of John Major, Gordon Brown and Tony Blair. His inside account of David Cameron’s premiership will be published next month.

Seldon tells the BBC Blair was more successful as a party leader winning elections than he was as a governing prime minister.

Fulfilment of his moderate reforming agenda was hampered for several years because of the antipathy of his chancellor, Gordon Brown, who increasingly resented Blair, and wanted him out of Downing Street so that he could take his place. This gave birth to the struggle that characterised the decade 1997-2007, between “Blairites” and “Brownites”.

“The former could be found on the centre-right of the party, the latter on the centre-left,” he says. “Many Labour supporters cannot forgive these two men for what they see as allowing personal acrimony to squander the best opportunity in a generation for advancing the cause of working people.”

But it’s Blair role in the Iraq war that remains his most controversial legacy.

“His support for US President George W Bush in the invasion of Iraq in March 2003 was the most disputed foreign policy decision by a British prime minister since Anthony Eden decided British troops should invade Egypt in 1956,” Seldon says. “The manner of Blair’s decision was hotly disputed, including question marks over whether he had misled the country to build his case for committing British troops.”

He might have been forgiven had the American-led invasion been a success, Seldon told the BBC, but its spectacular failure to bring peace to Iraq led to many years of recrimination.