Rebecca Long-Bailey warns Labour against backing an "establishment" candidate like Keir Starmer, in her clearest attack yet against the frontrunner to replace Jeremy Corbyn as party leader.Long-Bailey tells Business Insider that Boris Johnson will beat Labour again if the party makes the mistake of thinking "you [can just] put on a nice suit and be a bit suave and think that's a route into Downing Street."She also criticised Corbyn's campaign for telling voters that their "lives are terrible" while failing to offer enough to aspirational voters.Visit Business Insider's homepage for more stories.The Labour party will lose the next general election if it elects an "establishment" leader like Keir Starmer, the Shadow Business Secretary Rebecca Long-Bailey has told Business Insider, in her strongest attack yet on the frontrunner to replace Jeremy Corbyn.In a clear reference to Starmer, who is currently leading the race to become the UK's official opposition party leader, leadership candidate Long-Bailey said that Labour risks making the mistake of thinking "you [can just] put on a nice suit and be a bit suave and think that's a route into Downing Street."Long-Bailey warned that Boris Johnson's Conservative party would punish the party again at the polls if it picked someone associated with the "establishment" like Starmer."The Conservatives want to paint us as the establishment party and we need an anti-establishment candidatesomeone from a 'red wall' seat who understands why we lost and the feelings on the ground," she said."You just can't put on a nice suit and be a bit suave and thinks that's a route into Downing Street.""The Conservatives will love that if that's what choose to do as a party because they'll paint us as the establishment that's failing our communities."In a speech in Salford, northwest England on Friday, Long-Bailey did praise the Shadow Brexit Secretary for his "rigorous and detailed" scrutiny of the Conservative government's Brexit plans.However, she suggested that his determination to make Labour support a second Brexit referendum had alienated voters."We didn't win the electionand that was partly to do with Brexit and partly because too many voters thought we looked like just another bunch of politicians in Westminster," she said.Long-Bailey, who is Starmer's closest rival in the contest to succeed Jeremy Corbyn, said the other candidates in the race were failing to provide the "answers" Labour needs after suffering a crushing election defeat in December.Speaking about Starmer, Lisa Nandy, and Emily Thornberry, Long-Bailey said: "So far I haven't seen any answers to any of the questions that we are facing."A vision. A big idea for what the future might look like."Thornberry, the Shadow Foreign Secretary, was eliminated from the contest on Friday night after failing to secure the support of enough constituency Labour parties.Corbyn's Labour made the mistake of telling voters 'that they need to be saved and their lives are terrible.'Long-Bailey also criticised the failed election campaign led by her close ally and the current Labour leader Jeremy Corbyn.Long-Bailey told Business Insider that she thought Labour's campaign did not have a clear message for aspirational voters."I didn't think we had a message that really said anything [to those voters]" she said."I think we sometimes used negative language and talked about all the terrible things and how we were going to helpand it's right that we do that."But we need to realise that a lot of people aren't struggling in the extreme sense of the wordyeah they'd like to do better and be paid morebut they were quite happy with where they were."They didn't need to be told that they needed to be saved and that their lives were terrible."Long-Bailey said that Labour didn't have a clear "overarching" message during the campaign."You can have lots of policies in your manifesto," she said."But what you're supposed to do is have an overarching message which ties together what you'd actually do in government, and pick out key policies which are most popular and you think represent that."What we did was announce a policy every day and people got confused and overloaded by it. It wasn't that the policies were wrong because they were really transformative. We just didn't need to focus on all of them," she said.Long-Bailey's Labour would not oppose another Scottish independence referendumLong-Bailey, the MP for Salford & Eccles, will on Saturday participate in a hustings with the other leadership candidates in Glasgow, Scotland.One of the big dilemmas facing Labour's next leader is how to its rebuild support in Scotland. The party has just one MP north of the border after losing six seats at the December general election.Long-Bailey has previously said she would not stand in the way of Scotland holding a new independence.The Scottish Parliament last month passed a motion urging Johnson's government to begin talks on holding a new referendum this year, while recent polls suggest that a majority of Scots now support leaving from the UK.Long-Bailey told Business Insider that if Members of Scottish Parliament pass legislation calling for a new referendum, the response of a Labour Party under her leadership "would be not to stand in the way."She said: "If the Scottish Parliament passed a motion calling for a referendum, as a democratic party we couldn't stand in the way of that and say no to it."We are not in the government and it wouldn't be up for us to make that decision. But I'd make sure our position as a party would be not to stand in the way of that democratic processbecause we are a democratic party.She added: "But we would campaign for Scotland to remain part of the UK. We've got to recognise that just saying 'we want you to stay' isn't going to win the argument. We've got to address the fact that many people in Scotland feel regarded as some cousin which doesn't receive the support and resources they deserve."Join the conversation about this storyNOW WATCH: Extremists turned a frog meme into a hate symbol, but Hong Kong protesters revived it as an emblem of hope Click here to read full news..