A Labour win at this year’s election will improve the mood of “a downtrodden country”, Keir Starmer will say, as he hopes to inject a note of optimism into what is set to be one of the most bitterly fought campaigns in recent history. The Labour leader will set out his pitch to voters at a speech in the west of England on Thursday marking the beginning of what Labour believes will be a five-month lead-up to the election. After a series of policy U-turns which have left many Labour activists dismayed, Starmer will insist that the party will change the country should it return to power, thanks to its commitment to public service. But as his senior officials rush to finish the party’s manifesto by the end of this month, Starmer will warn his supporters not to hope for the kind of eye-catching policies they have promised in previous years, which he will dismiss as “gesture politics”. “It will feel different,” Starmer will say. “The character of politics will change, and with it the national mood. A collective breathing out, a burden lifted, and then, the space for a more hopeful look forward. Because the truth is, it’s this kind of politics and only this kind of politics that can offer real change.” He will add: “This year, at the general election, against the understandable despair of a downtrodden country, I will ask the British people to believe in it again.” Starmer’s speech marks a year since he and the prime minister, Rishi Sunak, gave competing speeches in London within a day of each other. While Starmer used his speech a year ago to launch five “missions”, which he said would guide Labour in power, Sunak made a more concrete set of five “promises”, only one of which – halving inflation – has been met. With Sunak having failed to boost growth, cut debt, cut NHS waiting lists or stop small boats crossing the Channel, he will host a more low-key event on Thursday, taking part in a question-and-answer session, which his party is not allowing national journalists to attend or cameras to broadcast in full. Starmer is hoping that voter disaffection with the Tories will propel him into Downing Street later this year. However his cautious tone on Thursday reflects concern among his senior advisers that voters have become so turned off by a series of political scandals that it will become difficult to motivate them to turn out at all. “You’re right to be anti-Westminster and angry about what politics has become,” Starmer will say. “But hold on to any flickering hope in your heart that things can be better, because they can, and you can choose it.” Senior Labour officials hope Starmer’s promise to lift the national mood will help dispel criticisms that the party is increasingly offering little in the way of more concrete change should it win the election. Party officials are now combing through Labour’s policy proposals looking for potential pitfalls as they finalise the manifesto before a possible spring election. The policy most in the spotlight is the pledge to spend £28bn a year on green projects, with several of those closest to Starmer warning that sticking to the promise will leave the party open to Tory attacks during the campaign. Sources also told the Guardian this week that Labour was likely to reverse its policy of introducing a five-year moratorium on former ministers lobbying for companies they once helped regulate, even as Starmer promises a broad clean-up of government ethics rules. While policy chiefs thrash out the final elements of the party’s election offer, Starmer himself will embark on a series of Q&A events in medium-sized towns, where his strategists believe the election is likely to be won and lost.