Rishi Sunak is facing an angry backlash from Tory MPs after the party suffered a “hammering” at the local elections.
The Conservatives are on course to lose up to 1,000 seats across England, with Labour and the Lib Dems enjoying major gains.
Keir Starmer said the results so far showed the country was “on course for a Labour majority at the next general election”.
Speaking to party workers at Labour HQ, he said: “We all know there’s no place for letting up. Let’s never mistake confidence for complacency.
“But we are going to bottle this feeling we have today and then we’re going to turn it into a general election win next year.
“We’re going to cut the cost of living, cut waiting times, cut crime. We’re going to end the Tory sticking plaster politics and we’re going to replace it with a mission-led Labour government that gives working people their future back.
“We’re going to do all that - together.”
Worried Tories said urgent improvements were needed if the party was to stand a chance when the UK goes to the polls next year.
Justin Tomlinson, the Tory MP for North Swindon - where Labour seized control of the local council - said it was “a dreadful set of results”.
“After so long, it was always going to be tough. But the Party collectively needs to take this as a wake up call to refresh and renew. We have to once again offer positive reasons to vote for us, at every level,” he tweeted.
John Redwood, the MP for Wokingham and a former cabinet minister, said: “Many former Conservative voters stayed at home in protest at high taxes, lack of control of our borders, and too much local and national government interference in their lives.
“If the PM wants to win back lost Conservative voters he should try offering some Conservative policies. Cut taxes, get better value for state spending and go for growth.”
Alan Jarrett, the Tory councillor who was ousted as leader of Medway Council in Kent by Labour, told Sunak to “get a grip”.
“I would tell them to get their act together on a number of fronts, to be quite honest,” he said.
Adam Stokes, was was deputy leader of South Kesteven council until the Tories lost control of the local authority, warned the party was facing a 1997-style wipeout at the next election.
“We should be returning back to our basic strategy of low tax and pro-growth,” he told BBC Politics Live. “It’s time the Conservative Party as whole reassess where we are going.”
Nigel Churchill, who lost his seat on Plymouth council as it fell to Labour, told the World at One that voters “do not trust” the Conservative government anymore.
He said the PM needed to “learn” why people had turned against the party and warned “we can safely say” it was heading for a general election defeat.
David Campbell Bannerman, the former Tory MEP who now runs the Conservative Democratic Organisation organisation which was set up by supporters of Boris Johnson, said the party “shouldn’t rule out” reinstating the former PM as leader.
“I don’t think we are giving our message across very well and people are very concerned about what we are doing and what we stand for,” he told BBC Radio 4′s Today programme.
“We are putting up taxes, the highest taxes for 70 years, and there is price to be paid for that.”
Campbell Bannerman also told Times Radio Sunak should submit himself to a “confirmatory vote” of the Tory membership.
Writing for Sky News, elections expert Professor Michael Thrasher said the Conservatives were suffering a “hammering”.
“If that trend continues, the party is likely to post a final tally that rivals the debacle of 1995 that left them limping towards a massacre at the general election two years later,” he said.
But speaking on Friday morning, Sunak vowed to push on with his agenda and not change course.
He said he was “not detecting any massive groundswell of movement towards the Labour Party or excitement for its agenda”.