Potential Labour leader Sir Keir Starmer has said the party has been making policies “without regard” for those in society who “want to get on”.
In what will be seen as a criticism of the party's direction under outgoing leader Jeremy Corbyn, the shadow Brexit secretary said the opposition party had failed to offer "opportunity" to voters in "recent years".
The party suffered its worst election defeat since 1935 during the December poll, losing 59 seats overall.
Sir Keir, speaking at an event in Stratford, said the party had labelled those in society either "the elite" or the "downtrodden" and had not done enough to appeal to those in between who "want to get on".
It comes as the Community union became the latest to back the early front-runner, who already has enough nominations from trade unions and socialist groups to make it on to the final ballot.
Monday, January 27 marked Sir Keir's first day back to campaigning in the leadership election since cancelling events on Thursday after his mother-in-law was admitted to intensive care following an accident last week.
Answering a question at the Old Town Hall about how Labour could win over Tory voters, Sir Keir said Labour needed to offer a more inspiring vision for future generations.
The Holborn and St Pancras MP said: "We've depicted the public as either elitist at the top or downtrodden, without regard for the middle where there are lots of people who want opportunity and we need to be making the case for solidarity and opportunity.
"I'm not sure we have been making both those cases powerfully enough. And I think if we do, we have the chance to bring over votes that we don't have at the moment."
The 57-year-old said his own toolmaker father and nurse mother had been "driven by the Labour dream that their children would have better opportunities than theirs".
Sir Keir also said he would "lead from the front" on tackling anti-Semitism if he is elected Mr Corbyn's successor on April 4.
The party is currently being investigated by the Equalities and Human Rights Commission over the blight of antisemitism in the party, a probe that Sir Keir said Labour must give "full access" to.
Speaking on the 75th anniversary of the liberation of Auschwitz, he said: "This is not complicated - if you're antisemitic, you shouldn't be in the Labour Party.
"If I was leader of the Labour Party, I would take personal responsibility for this. I would need to know every week what is going on.
"It is only when the person who is leading the party takes that kind of direct involvement that things get done and things change."
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