Angela Eagle is to delay her expected leadership challenge to Jeremy Corbyn, Labour sources have said.

The Wallasey MP and former shadow business secretary had been expected to declare that she was going to run as a "unity candidate" this afternoon at a news conference.

However sources said she had decided to hold off because of the turmoil engulfing the Conservatives following the shock withdrawal of Boris Johnson from the leadership race.

"She is still up for it. She has the signatures," one source said, referring to the 50 nominations from Labour MPs and MEPs needed to mount a challenge under party rules.

Ms Eagle had been expected to announce she was challenging Mr Corbyn after deputy party leader Tom Watson failed to persuade him to stand down following an overwhelming vote of no confidence by Labour MPs.

Her decision to wait gives the rebels more time to intensify the pressure on Mr Corbyn to quit of his own accord.

Crucially his supporters argue that as the incumbent he would automatically be on the ballot paper in the event of a challenge, with the prospect he could again mobilise the grassroots activists who propelled him to the leadership last year.

If he resigned, however, allies such as shadow chancellor John McDonnell might struggle to get the nominations they need to enter the leadership race.

There were further calls for Mr Corbyn to quit with a letter signed by 540 Labour councillors posted on the LabourList website saying he was "unable to command the confidence of the whole party nor of many traditional Labour supporters we speak with on the doorstep".

In a further indication of the mayhem within the Labour ranks, MP Rob Marris resigned from his role in the shadow Treasury team during the committee stage hearings on the Finance Bill.