Jeremy Corbyn will pledge to take on “vested interests holding people back”, as the Labour leader kicks off the party’s general election campaign.
In a speech on Thursday, Mr Corbyn will promise to “rebuild” public services and take on “the few who run a corrupt system”.
He will say the 12 December poll is a “once-in-a-generation chance to transform our country”.
However, Boris Johnson blamed him for refusing to allow Brexit to happen.
The prime minister said the UK’s failure to leave the EU by 31 October had been caused by Mr Corbyn “insisting upon more dither, more delay”.
Ahead of a series of campaign visits of his own on Thursday, the day Brexit had been scheduled to take place, Mr Johnson said: “I didn’t want an election.
“Like the country I wanted to get Brexit done, but it is the only way forward.”
“I want next year to be a great year for our country – with more investment in frontline NHS services, the recruitment of thousands more police officers to reduce violent crime and investment in every one of our primary and secondary schools across the country.”
Five weeks of official election campaigning are expected to get under way once Parliament is formally shut down next Wednesday, 6 November.
It comes after the House of Lords passed the legislation to authorise the election, which was approved by MPs on Tuesday.
Mr Corbyn is expected to say Labour will take on “tax dodgers, dodgy landlords, bad bosses and big polluters” in “the biggest people-powered campaign in history”.
“You know what really scares the elite? What they’re actually afraid of is paying their taxes. So in this election they’ll fight harder and dirtier than ever before”.
“They’ll throw everything at us because they know we’re not afraid to take them on.”
“We will invest in every nation and region, rebuild our public services and give our NHS, schools and police the money they need by taxing those at the top to properly fund services for everyone.”
But the Conservatives’ campaign chairman James Cleverly said: “A vote for Labour is not a vote for change. It is precisely the opposite.”
He said Labour would offer “more delay and uncertainty on Brexit, meaning the government can’t focus on people’s priorities, like the NHS, schools and crime.”
MPs standing down
Announcing that she would not contest her Loughborough seat again, she said being an MP had had a “clear impact” on her family.
“The abuse for doing the job of a modern MP can only be justified if, ultimately, Parliament does what it is supposed to do – represent those who serve in all areas of public life, respect votes cast by the electorate and make decisions in the overall national interest,” she wrote.
More than 50 incumbents are preparing to stand down – and there may be more announcements in the coming days.
Liberal Democrat leader Jo Swinson has defended her decision to campaign as a “candidate to be prime minister”, denying such an outcome is a fantasy.
Ms Swinson told the BBC’s Andrew Neil the UK was in a “very volatile political situation” and anything could happen on 12 December.
“Plenty of people said they did not think Jeremy Corbyn would become Labour leader or Donald Trump would become US president.
“Plenty of people said they did not think Brexit would ever happen,” she said.
“We have seen many unprecedented political results in recent years.”
What happens next?
- Having been approved by the Lords, the early election bill will receive Royal Assent – when the Queen formally agrees to the bill becoming law
- On Monday 4, November, MPs are due to elect a new speaker to replace John Bercow
- Just after midnight on Wednesday, 6 November, Parliament will be shut down or “dissolved” – meaning every seat in the House of Commons becomes vacant
- The electoral authorities have set a deadline of the end of Tuesday, 26 November for people to register to vote.
- The cut-off point to apply for postal votes is the same day, but at 17:00 GMT.