Image copyright PA Image caption Chris Leslie is to take the key role of shadow chancellor

Acting leader Harriet Harman has reshuffled Labour's shadow cabinet, replacing big names who lost their seats at the general election.

Chris Leslie replaces Ed Balls as shadow chancellor while Hilary Benn becomes shadow foreign secretary, succeeding Douglas Alexander.

Ian Murray, the party's only Scottish MP, becomes shadow Scottish Secretary.

Among other changes, Sadiq Khan leaves the shadow cabinet ahead of his bid to be Labour candidate for London mayor.

The timetable for replacing Ed Miliband as leader was discussed at a meeting of the Parliamentary Labour Party on Monday evening.

Ms Harman told MPs there were "balanced arguments" over whether a short or long campaign would be best.

No 'mourning'

She also told them their job was to "challenge and harry" the Conservatives "every step of the way".

"You are going to be getting up there and at them," she said.

"We have got to throw off any sense of loss or mourning.

"The SNP are going to be strutting down this corridor, they want to see us downcast, we're not going to give them that pleasure."

At the same time as the reshuffle, Labour peer Lord Sugar - who did not have a formal role - announced he was quitting the party.

Image copyright PA Image caption Sadiq Khan is leaving to focus on his bid to become Labour's London mayoral candidate

Image copyright Getty Images Image caption Hilary Benn is promoted to shadow foreign secretary

Image caption Lord Sugar said he had been "disillusioned" with Labour for some time

The businessman, who joined Labour in 1997, said he had "lost confidence" in the party because of its "negative business policies and the general anti-enterprise concepts they were considering if they were to be elected".

Lord Sugar, who was the party's enterprise adviser under Gordon Brown, said he had made the decision at the start of the year but had not disclosed it until after the election to avoid being seen to "stick the boot in" during the campaign.

Ms Harman is having to fill some notable gaps in Labour's top team after the party lost all but one of its Scottish MPs and unexpectedly saw other key figures such as Ed Balls lose their seats.

The likely leadership candidates to replace Ed Miliband - Andy Burnham, Yvette Cooper and Chuka Umunna - will all stay in their jobs shadowing health, home affairs and business respectively.

Mr Leslie steps up from his previous role as shadow Treasury secretary to take Mr Balls' place in the key post of shadow chancellor, while Mr Leslie's number two will be Shabana Mahmood.

Mr Benn will shadow foreign secretary Philip Hammond, while his old role as communities and local government spokesman will be taken by Emma Reynolds. Chris Bryant takes the job of shadow culture secretary vacated by Ms Harman.

Mr Khan will be replaced by former cabinet minister Lord Falconer while Jon Cruddas, who helped write Labour's election manifesto and Lord Wood - a key ally of Ed Miliband - are also stepping down.

Announcing his departure, Mr Khan said it was "an opportunity for others to take on a leading role as we start the fightback for 2020", adding that he would "decide how best I can contribute to the fight over the coming months and years".