LONDON (REUTERS) - Britain's opposition Labour Party faces annihilation if it elects hard left lawmaker Jeremy Corbyn as its next leader, former prime minister Tony Blair said on Thursday, urging party members not to back "policies from the past".

Voting begins on Friday in a four-way leadership contest triggered by a crushing election defeat in May. Opinion polls show Corbyn, who wants to steer the party sharply back towards its socialist roots, has a large lead over his rivals.

Writing in the Guardian newspaper Blair, a centrist who won three national elections for Labour between 1997 and 2005, warned that the prospect of Corbyn-led party had put Labour in"danger more mortal today than at any point in the over 100 years of its existence". "The party is walking eyes shut, arms outstretched, over the cliff's edge to the jagged rocks below," he wrote.

"If Jeremy Corbyn becomes leader it won't be a defeat like 1983 or 2015 at the next election. It will mean rout, possibly annihilation."

The stark intervention is Blair's second in the leadership race, having previously told supporters that elections could not be won from a left-wing platform.

"Jeremy Corbyn doesn't offer anything new," Blair wrote on Thursday. "These are policies from the past that were rejected not because they were too principled, but because a majority of the British people thought they didn't work."