LONDON (Bloomberg) - London Mayor Sadiq Khan called on members of Britain's opposition Labour Party to oust Mr Jeremy Corbyn as their leader in a vote that starts on Monday (Aug 22), saying Mr Corbyn is "extremely unlikely" to lead Labour back to power.

Mr Khan, who is the most powerful Labour politician to hold elected office, called on Labour members to support Mr Corbyn's challenger Owen Smith.

Mr Corbyn failed to "show the leadership we desperately needed" during the campaign for the referendum on Britain's European Union membership, Mr Khan wrote in Sunday's Observer newspaper. "Why would things be different in a general election?" he said.

Since the Brexit vote, most members of Mr Corbyn's team of parliamentary spokesmen have quit and he has lost a confidence vote among Labour lawmakers, prompting Mr Smith to challenge him. Most recent opinion polls show the Conservatives under new Prime Minister Theresa May more than 10 percentage points ahead of Labour.

"Jeremy's personal ratings are the worst of any opposition leader on record - and the Labour Party is suffering badly as a result," Mr Khan said. "I am afraid we simply cannot afford to go on like this."

Even so, many rank-and-file Labour members remain supportive of Mr Corbyn, and bookmakers make him the clear favorite to retain the leadership.

Ballot papers will be sent out starting on Monday, with the result due to be announced on Sept 24.

The Sunday Times newspaper reported that opponents of Mr Corbyn are planning to set up a rebel group in Parliament to coordinate defiance of the leader if he is re-elected.