Former British Prime Minister Tony Blair is warning the Labour Party that adopting an "old-fashioned leftist platform" of tax-and-spend policies will lead to electoral oblivion.

Labour is seeking a new leader to rebuild after losing badly in May's election to the Conservatives. Left-wing lawmaker Jeremy Corbyn has gone from longshot to serious contender — to the horror of party chiefs.

Blair said Wednesday Labour should move on "but for heaven's sake, don't move back."

Corbyn accuses rival candidates of offering "austerity light" policies that provide no alternative to the Conservatives. His message has found strong support among party members, making him a front-runner.

Some Labour lawmakers have said they will try to oust Corbyn immediately if he wins the party ballot, whose result will be announced Sept. 12.