A former special advisor to Tony Blair says a decision to allow Jeremy Corbyn the automatic right to defend his leadership will be the death of the Labour party.
John McTernan is a long-time critic of Mr Corbyn and said if the leader "had any shame" he would have walked away some time ago.
He told BBC News in the wake of the NEC's secret ballot decision: "Today was the day the Labour party was stabbed in the heart and killed by the Labour National Executive Committee.
"Jeremy Corbyn may have won this vote, but he has destroyed the Labour party," he said.
"This is the end of the Labour party, nothing more or less than that, and it is a terribly sad day for anybody who believes in opposition to the Tories, anybody who believes in the history of the Labour party and all it has achieved."
The NEC ruled by a reported majority of four that an incumbent leader has the automatic right to stand in a leadership ballot, crushing the hopes of the majority of the party's MPs that they could have a leadership election without Mr Corbyn on the ballot.
Labour appoints its leader by a vote of its members, many of whom - among the grassroots at least - are passionate supporters of the Islington MP.
But if the NEC ruling had gone against him, Mr Corbyn would almost certainly have failed to win the 51 nominations normally required to make it onto the ballot.
Speaking after the decision was announced, Mr Corbyn said he was "delighted" and sounded a defiant tone.
As his supporters cheered, he told reporters: "I'm sure Labour MPs will understand that the party has to come together in order to present to the British people the options of a different and better way of doing things."
Angela Eagle, the former shadow business secretary who has emerged as the leading challenger to Mr Corbyn, issued a brief statement saying she was "determined" to beat him.
She said: "I'm glad Labour's NEC has come to a decision. I welcome the contest ahead. And I am determined to win it."
When the news broke, crowds gathered outside a fundraiser to support Mr Corbyn cheered and clapped in jubilation.
Around a thousand people attended the Keep Corbyn event in Kentish Town, north London, on Tuesday evening while a crunch meeting of the party's ruling committee was under way.
Adam Booth, 30, a member of the Socialist Appeal, who attended the fundraiser said he was "delighted".
"It's the only democratic decision that could have really succeeded."
