Successive Labour leaders made a mistake in telling voters Tony Blair was "crap", a former senior adviser to Ed Miliband has said.
Tom Baldwin, who served as the former Labour leader's director of communications, warned on Saturday that the public was not convinced by the party distancing itself from its past.
"I’ll say here what I said privately then, failing to defend our record with consistency and passion was a mistake," he told the Fabian Society conference in central-London.
"You would not catch the Tories doing it any more than you would find a car manufacturer trying to sell you a new model with adverts saying all its recent cars have been crap," he said.
"But that is what voters hear when three successive Labour leaders have, in different ways, spent their time telling the world what’s wrong with Tony Blair."
Baldwin added the party was now "back in year zero" as it was arguing with itself rather than targeting the Conservative Party.
The warning was echoed by Labour MP Wes Streeting, who said: "The penny has dropped. Turns out trashing your own record doesn't incline people to give you another go."
Speaking at the same event, Labour MP Keir Starmer told Labour to "stop squabbling about the micro-tactics of the hear and now".
Former deputy leadership candidate Stella Creasy said while Labour needed to be united, there was no point being unified with no real purpose.
"If the Labour Party didn't exist today - would we invent it? There is no legal requirement to maintain us. Unless we can answer that are we wasting each others time? Like two bald men fighting over a comb?" she said.
"Yet too much now rests on being united by what we are not - mainly not being the Tories, sometimes not the nationalists, and God forbid the liberals.
"That does not make us the alternative government in waiting. It doesn't even really make us the opposition. It just makes us 'not them'.
"Mocking those who voted for others only reinforces this problem. Share all the Facebook statuses and memes you want - it doesn't speak to who WE are or why anyone should care.
"No one has the preserve on being right- not the Fabians, Progress, not the Co-op, not Momentum. Not even Owen [Jones]. But if we choose to work together in this way, we can bring out the best in each other."Suggest a correction