Opinion polls show the centre-left Labour Party is set for a big win in Thursday's vote that would end 14 years of Conservative government and hand Starmer the keys to the prime minister's Number 10 Downing Street office on Friday morning.
Both Starmer and Conservative Prime Minister Rishi Sunak kicked off the last day of campaigning before polls open warning voters of dire economic consequences if the other man wins.
But, facing predictions of the worst result in the party's history, the Conservatives turned their focus to damage limitation, saying they needed to hang on to enough seats to provide an effective opposition to a Labour government.
"I totally accept that where the polls are at the moment means that tomorrow is likely to see the largest Labour landslide majority, the largest majority that this country has ever seen," Conservative minister Mel Stride told the BBC.
"What therefore matters now is what kind of opposition do we have, what kind of ability to scrutinise government is there within parliament."
Asked abour Stride's comments, Sunak told ITV: "I'm fighting hard for every vote".
Polling analysis by Survation sees Labour winning 484 of the 650 seats in parliament, far more than the 418 won by the party's former leader Tony Blair in his 1997 landslide victory, and the most in its history.
The Conservatives were predicted to win just 64 seats, which would be the fewest since the party was founded in 1834.
Other analyses have shown smaller margins of victory for Labour, but none have shown a different overall outcome.
GET THE VOTE OUT
Labour's final campaign push focused on their fear that voters could see the result as a foregone conclusion and stay at home during polling on Thursday, or register protest votes with smaller parties.
Starmer said Stride's comments were an attempt to lure wavering voters into not casting their ballots after polling opens at 0600 GMT.
"I say: if you want change, you have to vote for it. I want people to be part of a change. I know there are very close constituencies across the country," he told the BBC.
"I don't take anything for granted, I respect the voters, and I know that we have to earn every vote until 10 o'clock tomorrow night and we will do that."
Starmer's campaign has been built around a one-word promise of 'change', tapping into discontent at the state of Britain's stretched public services and falling living standards - symptoms of a sluggish economy and political instability.
Sunak has sought to persuade voters that his 20 months in charge have set the economy on an upward path after the external shocks of COVID-19 and the war in Ukraine, and drawn a line under years of turmoil overseen by his Conservative predecessors.
He says Starmer will have to put up taxes to implement his agenda for change and the bigger Labour's win, the more emboldened Starmer would be to raise taxes beyond those he has already outlined.
Having failed to close Labour's roughly 20-point opinion poll lead, Sunak turned to former prime minister Boris Johnson - the man he helped turf out of office in 2022 - inviting him to speak at a late night Conservative Rally on Tuesday.
Johnson, one of British politics' most recognisable figures and the man who delivered the party a landslide win in 2019, made his first big public appearance of the campaign with a speech which listed many of his own achievements and gave little personal endorsement to Sunak.
"None of us can sit back as a Labour government prepares to use a sledgehammer majority to destroy so much of what we have achieved," he said.
