First his brother was defeated. Now his former boss is disowned

Ed Miliband will today list Labour's mistakes during its 13 years in power and promise not to repeat the arrogance and hubris of Gordon Brown's boast that he had abolished "boom and bust".

In his first keynote speech to the Labour conference as the party's leader, he will distance himself from Mr Brown, for whom he worked as an adviser for 10 years before becoming an MP, in an attempt to draw a line under the Blair-Brown era.

He will admit that New Labour was wrong to allow "light-touch" regulation of the City of London and to let people build up huge levels of debt.

"The new generation is different – different attitudes, different ideas, different ways of doing politics," Mr Miliband will tell the Manchester conference. In a personal speech, he will outline how his core values and beliefs were shaped by his parents' experience as refugees from Nazi-occupied Europe.

Three days after his dramatic victory over his elder brother, David, in the Labour leadership election, Mr Miliband will try to heal the party's wounds and reassure Blairites by promising to keep Labour in the centre ground.

However, some Blairites are furious that he has pronounced the New Labour era over, believing that sends a wrong signal to the middle-class voters who have deserted the party. "It's a recipe for staying in the political wilderness," one shadow minister said yesterday.

A new poll last night placed Labour ahead of the Tories for the first time in three years. According to the YouGov survey for The Sun, support for Labour has risen to 40 per cent with the Conservatives on 39 per cent and Liberal Democrats languishing on 12 per cent.

Blairites are urging the new leader to show he is not a prisoner of the trade unions, who secured his narrow victory on Saturday. They want him to reform the way that the Labour leader is chosen, with one option being to abolish the union section of the electoral college. At the moment the electoral college is made up one-third of MPs, one-third of Labour Party members and one-third of affiliated unions' members.

Under the change, party members and MPs would have half the votes each, with the unions urged to persuade their members to join the party so they retained a vote. Andy Burnham, the shadow Health Secretary and leadership contender, is backing this idea.

Another proposal is for the Labour leader to be chosen by a pure "one member, one vote" system – abolishing the current sections for MPs and unions. The votes of an MP would be worth the same as an ordinary party member and people could not have more than one vote, as they can under the present system by belonging to a union or other affiliated bodies.

Some Blairites want Mr Miliband to make Labour less dependent on funding from the unions, who contribute more than 90 per cent of its income. Unions could be covered by a cap on donations agreed with other parties under a plan to "take big money" out of politics and reward parties who attracted small donations with matching pound-for-pound support from taxpayers.

David Miliband, who won an ecstatic response yesterday when he urged the conference to unite behind his brother, is still deciding whether to leave the Labour front bench or serve under him in the Shadow Cabinet. He is expected to announce his decision tomorrow. "It's a really tough decision; he wants to do what is right for Ed rather than himself," one close ally said last night.

In his address, Ed Miliband will try to launch Labour's fightback following its defeat at the May general election by showing humility about the mistakes which led the party to lose the trust of voters.

His message to them will be: "When you saw the worst financial crisis in a generation, I understand your anger that Labour hadn't stood up to the old ways in the City which said deregulation was the answer.

"When you wanted to make it possible for your kids to get on in life, I understand why you felt that we were stuck in the old thinking about higher and higher levels of personal debt, including tuition fees. And when you saw jobs disappear and economic security undermined, I understand your anger at a Labour government that claimed it could end boom and bust."

Although Ed Miliband will stop short of a formal apology, his words mark a significant departure from Labour's previous attempts to blame the recession on the global financial crisis. Opinion polls show the voters believe Labour is at least partly responsible and Mr Miliband judges that he must address that before the party can regain credibility on the economy.

Today he will admit that the previous government lost its ability to adapt in response to changes in the world. "Too often we bought old, established ways of thinking and sometimes we even became the establishment," he will say.

After praising the achievements of Labour in office, he will argue: "It was courage that made us such a successful force. But our journey must also understand where it went wrong.

"How did a party with such achievements to its name end up losing five million votes between 1997 and 2010? The hard truth is that a party that started out by taking on old thinking became the prisoner of its own certainties."

The Labour leader will promise that the new generation he symbolises will make the party "a force that takes on established thinking, speaks for the majority and shapes the centre ground of politics".