LONDON (Reuters) - Keir Starmer, the frontrunner in the race to lead Britain's main opposition Labour Party, has pledged to end feuding within its ranks and take the fight to Prime Minister Boris Johnson if he wins the contest.
Labour leader Jeremy Corbyn has said he will step down after the party's worst general election performance since 1935 handed Johnson's Conservatives, or Tories, a large majority in parliament.
The Corbyn era, which began in 2015 when the veteran socialist unexpectedly won the leadership, was marked by bitter infighting between the party's leftist and centrist wings.
"We cannot fight the Tories if we are fighting each other. Factionalism has to go," Starmer, 57, said on Saturday in a speech in Manchester, northern England, to formally launch his leadership campaign.
Starmer urged party supporters to stop attacking the achievements of the Labour governments led by Tony Blair and then Gordon Brown between 1997 and 2010, and not to dismiss Corbyn's record.
"We are not going to trash the last Labour government, but nor are we going to trash the last four years," he said. "There have been very many important moves."
Despite winning three successive general elections -- the only Labour leader to do so -- Blair is unpopular with many within Labour who say he betrayed the left and led the country into a disastrous war in Iraq. "Blairite" is considered an insult by those on that wing of the party.
Centrist Labour supporters say Corbyn's radical agenda, which included sweeping nationalizations, failed to win over the electorate. They used "Corbynista" as a negative label.
Starmer, a former Director of Public Prosecutions, was Labour's Brexit policy chief under Corbyn.
He pushed for a second referendum on whether Britain should leave the European Union, but has said that the result of the December general election had "blown away" that argument and Labour should now move on.
He said the future focus should be on ending fiscal austerity, investing in public services, and winning public arguments against Johnson, whom he described as lacking principles and a moral compass.
"I've never known a time when a radical Labour government was so needed," said Starmer.
In the first stage of the party leadership contest, candidates must seek the backing of fellow Labour members of parliament.
Starmer has received 68 nominations so far, a long way ahead of his nearest rival, Corbyn loyalist Rebecca Long Bailey, who has 26 nominations.
He also has the backing of Unison, the public service workers' union, which is seen as a crucial endorsement.
The overall winner in the contest, in which grassroots party members will cast their ballots, will be announced on April 4.
(Reporting by Estelle Shirbon; editing by Mike Harrison)