Labour leadership election: Jeremy Corbyn supporters boo mention of Sadiq Khan at rally

The Mayor had criticised Mr Corbyn and backed his rival Owen Smith

Supporters of Jeremy Corbyn booed and jeered a mention of Labour’s London Mayor Sadiq Khan on Sunday night, underlining tensions within the party.

The Labour leader held a rally of thousands of supporters on Sunday in north London, as ballot papers for the party’s leadership contest were sent out.

But the 4,000 capacity venue Ruach City Church in Kilburn, north London, erupted in angry booing when Mr Khan’s name was mentioned.

“Despite what Sadiq Khan says. We won London under Jeremy Corbyn’s leadership,” NEC member Claudia Webber had told the audience, according to the Huffington Post – causing some supporters to erupt.

The angry reaction stems from criticism of Mr Corbyn by Mr Khan. The Mayor, who nominated Mr Corbyn for leader in 2015, said he backed challenger Owen Smith to lead the party.

In his piece for the Observer, Mr Khan said his leader did not have the qualities needed to take the party to success.

“By every available measure, if Jeremy remains as leader, Labour is extremely unlikely to win the next general election,” he said.

“The hopes of the members who have joined our party would be dashed again. Jeremy has already proved that he is unable to organise an effective team, and has failed to win the trust and respect of the British people.

(Getty Images (Getty Images)

“Jeremy's personal ratings are the worst of any opposition leader on record - and the Labour party is suffering badly as a result. He has lost the confidence of more than 80% of Labour's MPs in Parliament - and I am afraid we simply cannot afford to go on like this.”

Mr Corbyn told the rally: “I am so proud that our party is now the biggest in Europe with over half a million members. Unlocking the potential of every single member, taking our message of hope into every community across the country, is at the heart of my plan to win the next general election so we can rebuild and transform Britain so no one and no community is left behind.

“I hope members and supporters cast their vote for us in this leadership election but after that, commit themselves to become active in our party, if they're not already. This election is not about one individual, but about all of us, and what we can achieve together.”

More than 640,000 members and supporters will be eligible to vote in the Labour leadership contest between Mr Corbyn and Mr Smith, the party has said.

As the first ballot papers were being sent out the party estimated there were 343,500 fully paid up members entitled to a vote in the election.

Their numbers will be supplemented by 129,000 registered supporters who made a one-off payment of £25 last month so they would be able to vote.

A further 168,000 affiliated supporters who are members of affiliated organisations such as trade unions also have a vote - although that number is expected to rise as the unions are still processing some 20,000 applications.

More than 50,000 applications to become registered supporters were rejected for "technical reasons" - such as duplicate applications, where people hit the refresh button on the online form multiple times, or failure to make the payment deadline.

Party members will receive their ballots by post as well as an email with an online ballot code, giving them a choice as to how they vote, but supporters will receive only an online ballot.

Online voting codes will be sent out during the course of Monday, Tuesday and Wednesday although Labour said the numbers involved meant that it would be "a number days" before all the ballot papers had been dispatched.