The Eagle has hovered but not yet landed. Yesterday evening Angela Eagle's team briefed that she would launch her leadership challenge at 3pm today. A senior MP told me: "the overwhelming view of the PLP is that she is the one to unite Labour." But by this lunchtime it had become clear that Eagle wouldn't declare today.

The delay is partly due to the hope that Jeremy Corbyn may yet be persuaded to resign. Four members of his shadow cabinet - Clive Lewis, Rachel Maskell, Cat Smith and Andy McDonald - were said by sources to want the Labour leader to stand down. When they denied that this was the case, I was told: "Then they're lying to their colleagues". There is also increasing speculation that Corbyn has come close to departing. "JC was five minutes away from resigning yesterday," an insider said. "But Seumas [Milne] torpedoed the discussions he was having with Tom Watson."

Some speak of a potential deal under which Corbyn would resign in return for a guarantee that an ally, such as John McDonnell or Lewis, would make the ballot. But others say there is not now, never has there ever been, any prospect of Corbyn departing. "The obligation he feels to his supporters is what sustains him," a senior ally told me. Corbyn's supporters, who are confident they can win a new leadership contest, were cheered by Eagle's delay. "The fact even Angela isn't sure she should be leader is telling, JC hasn't wavered once," a source said. But her supporters say she is merely waiting for him to "do the decent thing".

Another reason for the postponement is a rival bid by Owen Smith. Like Eagle, the former shadow work and pensions secrtary is said to have collected the 51 MP/MEP nominations required to stand. Smith, who first revealed his leadership ambitions to me in an interview in January, is regarded by some as the stronger candidate. His supporters fear that Eagle's votes in favour of the Iraq war and Syria air strikes (which Smith opposed) would be fatal to her bid.

On one point Labour MPs are agreed: there must be just one "unity candidate". But after today's delay, a challenger may not be agreed until Monday. In the meantime, the rebels' faint hope that Corbyn may depart endures.