London - Britain's Labour opposition is facing a battle for its future direction after a bruising general election defeat, with surviving lawmakers gathering for the first time on Monday to assess the damage.Rival factions are already jockeying for control of the centre-left party as Labour starts picking a new leader to replace Ed Miliband, who quit on Friday following their election flop.As jubilant Conservative Prime Minister David Cameron named his new government, Labour leadership contenders were thrashing out why key voters deserted them.Interim leader Harriet Harman told BBC radio the party needed to study the facts of its defeat."The truth is there's not a snap answer. We have to do some serious thinking," she said, as she began appointing a new frontbench team.Tony Travers, professor of politics at the London School of Economics university, told AFP that Labour "wasn't able to sell an alternative vision" to the electorate."The big question for the left in Britain is what do they have to do... to be credible and come up with an alternative proposition?"Labour needs to work out where to go after suffering catastrophic losses in Scotland to left-wing nationalists, while crucial middle-class English voters swung even further behind the Conservatives.Meanwhile in Labour's post-industrial English heartlands, support haemorrhaged to the populist UK Independence Party.Call for aspirational approachLabour moderates savaged Miliband's approach over the weekend, saying he had a narrative for what Labour would do to the rich and for the poor, but nothing for the majority in between.Former Prime Minister Tony Blair, who led Labour to three straight general election victories in 1997, 2001 and 2005, urged the party to reclaim the centre ground he successfully occupied."Labour has to be for ambition and aspiration as well as compassion and care," he wrote in The Observer newspaper."'Hard-working families' don't just want us to celebrate their hard work; they want to know that by hard work and effort they can do well, rise up, achieve."Alistair Darling, Labour's former finance minister, told BBC radio: "We were not convincing."We did not have an economic policy."Business magnate Alan Sugar, who was made Labour Prime Minister Gordon Brown's "enterprise tsar" in 2009, announced on Monday he was quitting the party."I found myself losing confidence in the party due to their negative business policies and the general anti-enterprise concepts they were considering if they were to be elected," he said.Only Liz Kendall, the party's spokesperson on care and elderly, has declared her candidacy for the leadership.She and probable rivals Chuka Umunna, the business spokesperson, and education spokesperson Tristram Hunt have all advocated a more aspirational approach.Health spokesperson Andy Burnham and home affairs spokesperson Yvette Cooper are also thought likely contenders.Bookmakers have Umunna as the 2/1 favourite, followed by Burnham at 5/2, Cooper at 5/1, Kendall at 7/1 and Hunt at 8/1.Meanwhile there was still no trace of the much-mocked "EdStone", a 2.6m high monument with generic-sounding Labour election pledges carved in stone.Unveiled by Miliband in a car park on May 3, the monolith was destined for the 10 Downing Street garden if Labour won office but has now vanished, despite a media hunt.Harman said: "I don't know where it is and I don't know what's going to happen to it either and it actually doesn't matter."