Keir Starmer has promised to “fight fire with fire” against Conservative attacks this year, setting up what is likely to be one of the longest and most bruising general election campaigns in recent history. The Labour leader said on Thursday he would not shy away from aggressive campaign tactics, hours after Sunak indicated he was planning to go to the polls in the second half of the year. “If the government want to put fire into their attacks, we will meet their fire with fire, because the stakes at this election are so high for working people,” Starmer told Sky News after his new year speech in Bristol. “They will go low. What I’m saying is if they want to go with fire into this election, we will meet their fire with fire.” Labour and the Conservatives are sharpening their attacks on each other in advance of the campaign to come. On Thursday, Sunak gave his clearest indication yet of the election date, saying it was his “working assumption” that he would call it later in the year , after weeks of speculation that he might do so in May instead. “I want to keep going, managing the economy well and cutting people’s taxes, but I also want to keep tackling illegal migration,” Sunak said. “I’ve got lots to get on with and I’m determined to keep delivering for the British people.” Labour officials dismissed Sunak’s comments as misdirection, insisting they would continue planning for a spring election. “Nothing has changed,” said a senior party official. “Sunak doesn’t want to tie himself in. But if my son told me his working assumption was that he would get his homework done today, I would not take that seriously.” Starmer accused the prime minister of “squatting in Downing Street for months on end, dithering and delaying while the country wants change”. “We’re ready for a general election, I think the country’s ready for a general election,” he told the BBC. “The prime minister is now hinting, without setting a date, that it might be later in the year. What’s he hiding? Why can’t he set a date?” Conservative MPs, however, believe Sunak is serious about waiting until almost the last minute to call a vote that could see him ejected from Downing Street. “I think he’s right to push it,” said one. “Yes, things are likely to get worse in the year to come. But still, you don’t walk into certain death – even if there is the prospect of worse death down the road.” Senior Tory sources said the party had not even yet set a deadline for completing its manifesto, adding further weight to Sunak’s claims to be aiming for an autumn election. Labour enters the election year 18 points ahead in the polls, but with big questions outstanding over how it would govern if elected. Party officials are wrangling over significant policy issues such as whether to remain committed to their pledge to spend £28bn a year on green investment by the end of the next parliament. Starmer defended the party’s green credentials on Thursday, but admitted the £28bn pledge would be at risk if it stopped Labour bringing down government debt levels. He added that the party’s main ambition was to decarbonise Britain’s power sector by 2030, though experts doubt whether that can be achieved without the scale of public investment the party has previously promised. The Labour leader added that his government would bring hope to a “downtrodden” country, adding: “To truly defeat this miserabilist Tory project, we must crush their politics of divide and decline with a new Project Hope.” His later comments about the tone of the campaign, however, hint at the intensity of the political attacks that are likely to feature prominently during the year to come. Starmer said in his speech he expected the Conservatives to unleash a “gauntlet of fear” before the election. The Tories have been poring over Starmer’s record as a human rights lawyer and director of public prosecution for material to use against him. Recent press stories have focused on how Starmer acted for the radical cleric Abu Qatada in his 2008 bid to avoid deportation to Jordan, and how he defended a convicted arsonist accused of terrorising his family. The Conservatives have also been keen to highlight issues of culture and identity, including asylum and trans rights, in an effort to put Labour on the wrong side of public opinion. Meanwhile Starmer has defended a Labour advertisement last year which accused Sunak of not supporting the incarceration of adults convicted of sexually abusing children. David Blunkett, the former Labour home secretary, described that attack as “gutter” politics. The attacks have become so intense that Justin Welby, the archbishop of Canterbury, recently called for political leaders to avoid divisive tactics. “We have to say: ‘My opponent is never my enemy. My opponent is always my fellow human being. We disagree profoundly, we disagree on incredibly important things, but they’re human,’” he told the BBC in December. Starmer will now spend the next few weeks touring the country holding question-and-answer sessions in a series of mid-sized towns as he takes his pitch to the country, while Sunak will hold a similar event on Friday in the north-west.