Sir Keir Starmer will promise to get Labour “back in business” when he delivers his first speech as leader to the party’s full conference.
Urging activists to unite to win the next election, he will launch an attack on Boris Johnson over his handling of the pandemic and the fuel crisis.
Sir Keir will also pledge to train thousands of teachers and cut waiting times for mental health services.
Rows between the leadership and left-wingers have dogged the conference.
They have clashed over the nationalisation of energy industries, leadership election rules and the level of the minimum wage – with a member of the shadow cabinet quitting in protest at Sir Keir’s stance on this.
Sir Keir is under pressure to unite his party and set out a vision that appeals to voters that have turned away from Labour.
It will be the first time he has addressed a full conference since becoming leader last April, because last year’s event was held online due to Covid.
BBC political editor Laura Kuenssberg said Sir Keir faced a “genuinely massive moment”, adding: “There’s always been a frustration that he has not had the chance to set out his vision, so today represents a shop window and it’s an opportunity he cannot afford to throw away.”
Sir Keir will deliver what aides have called a “personal” speech in the Brighton Centre, setting out his principles and urging his party to show more discipline to beat the Conservatives.
He will say: “The questions we face in Britain today are big ones: how we emerge from the biggest pandemic in a century, how we make our living in a competitive world, the climate crisis, our relationship with Europe, the future of our union.
“These are big issues, but our politics is so small. So our politics needs to grow to meet the scale of the challenge.”
With Labour having lost four general elections in a row, the last one by the biggest margin since the 1930s, Sir Keir will attempt to distance himself from his predecessor Jeremy Corbyn.
A Labour source said the speech would be “more optimistic, more focused on the future, more outward-looking” than others in recent years.
The speech will be “a clear indication that Labour will never again go into an election with a manifesto that isn’t a serious plan for government”, they added.
Describing mental health support as “one of the urgent needs of our time”, he will promise to provide treatment within a month for all those in England who require it.
He will also pledge to take on 8,500 more mental health staff so that an extra million people a year can get help, with specialist “hubs” being set up to assist young people.
Labour says it will fund the measures by closing tax loopholes for private equity fund managers and removing the VAT exemption from private schools.
On education, Sir Keir will promise to take on “thousands” of extra teachers in England – his aides did not provide a more specific figure.
There will be more help for pupils who are currently leaving school without qualifications, while the inspection body Ofsted will be reformed to offer more support to struggling schools, he will say.
‘Massive opportunity’
Labour has lagged behind the Conservatives in most recent opinion polls, despite the government running into trouble over fuel supplies and soaring energy bills.
Gary Smith, general secretary of the Labour-supporting GMB union, told the BBC that the speech gave Sir Keir a “massive opportunity” to cut through to voters.
Policies already announced at the conference include borrowing £28bn to make the UK economy greener, extending the school day and putting more police officers on the beat.
But Mr Smith called for “clearer and sharper commitments”, adding: “Too much of the stuff this week has been insipid. We’d like to see things far firmer, as that’s what’s going to generate support in working-class communities.”
There is a sense in Brighton this week that Labour is, broadly, moving to a new reality or perhaps returning to something that’s more familiar.
The left screams and shouts. The party machine and its leaders, more in the centre, listen “respectfully” then ignore much of what is said.
That’s the reverse of what happened under Jeremy Corbyn, when the right of the party howled, the party machine and its leaders listened “respectfully” then ignored much of what was said.
Sir Keir’s speech comes at the end of a five-day conference dominated by rows between the party’s left wing, including supporters of Mr Corbyn, and members loyal to the leader.
On Monday, shadow employment secretary Andy McDonald quit Labour’s front bench, saying he had been ordered to argue against raising the minimum wage to £15 an hour.
The next day, the conference backed a motion calling for this to be party policy, although this is not binding on the leadership.
And delegates voted in favour of nationalising the UK’s energy industry, despite Sir Keir ruling this out.
The leader also angered the left when he pushed through changes to the way Labour elects its leaders, including candidates needing the support of 20% of MPs – rather than the previous 10% – before they can run for the leadership.
His opponents said this was an attempt to subvert democracy, but the leadership insisted it was a “major step” towards winning the next general election.