Ed Miliband has vowed to turn his fight to win back a Labour seat after Tory MP Louise Mensch stood down into a "crusade for young people".
The Labour leader was in Thrapston, near Corby in Northamptonshire, where he pledged the party would knock on every door in a bid to win votes in a forthcoming by-election.
A cheer went up from some of the 30 gathered Labour supporters when he told them he would make unemployment a key battleground issue in the campaign.
He told the group: "I make this promise about this campaign - we are going to be visiting every door in this campaign, whether people voted Tory, Liberal Democrat, Labour or didn't vote at all. Less than half the people voted at the last council election - we've got to reach out to them.
"We've got to reach out to people who are turned off politics. We've got to make this campaign, and we are going to make this campaign, a crusade for the young people of Corby, a crusade for people right across Corby."
Mr Miliband was in the Corby and East Northamptonshire constituency to launch his party's campaign to try to snatch the seat from the Conservatives.
Prime Minister David Cameron, whose party is at a low ebb in the polls against a resurgent Labour, faces a stiff challenge to retain Mrs Mensch's seat, but the Conservative vote has remained strong in recent council elections.
Mrs Mensch - then Louise Bagshawe before her marriage last year - won by only 1,951 votes in the 2010 general election. Labour had previously held the constituency since 1997.
Mr Miliband, who was in Corby less than three weeks ago, was joined by Labour's prospective parliamentary candidate Andy Sawford, as he met a group of young people at a cafe before talking to locals in the centre of Thrapston.
He said the Labour Party would fight for jobs, businesses, people worried about public sectors such as the NHS and policing, and young people who want to find jobs. He conceded it would be a "tough fight" to win the seat back from the Tories but said the party was determined to work for every vote.