Ed Miliband launches Labour's Corby by-election campaign
Ed Miliband has delivered "a message of hope" to voters in Corby at the launch of his party's by-election campaign.
Mr Miliband said he wanted people to trust Labour again and promised to reach out to "everybody in Corby".
Louise Mensch, who has held the seat since 2010, is stepping down and moving to New York with her family.
The by-election is expected to be held in November. Labour's candidate will be Andy Sawford, the son of former Kettering MP Phil Sawford.
Mr Miliband said Labour had a "very tough fight" on its hands but said his party could make a difference to people's lives.
"We can put our young people back to work by taxing bankers' bonuses. We can take action to force the energy companies to give people a fairer deal. We can reform our banks so they better serve small business.
"And we can deliver an NHS focused on the needs of the patients even in tough times. So that's who we are fighting for."
He attacked the government's record on youth unemployment, saying they were making young people's lives worse.
"Young people who are desperate to work," he said.
"Young people who want to make a contribution to our country and want to do better for themselves but can't because Government is not letting it happen."'Not all the same'
He said in the run-up to polling day Labour - who suffered a shock defeat at the hands of Respect's George Galloway in Bradford West earlier this year - would try to visit every home in the constituency.
"Our opponents in this by-election are not just the Tories and Lib Dems but those who think that politics cannot make a difference.
"The last time there were council elections here in Corby less than half those eligible to vote did so. We all hear it on the doorsteps. People who say all politicians are the same. Who say that voting won't make any difference."
Mrs Mensch has been a prominent face among the 2010 intake of MPs, known for her activities on the culture, media and sport select committee and her Twitter presence.
She said she had decided to step down after finding it increasingly difficult to juggle family responsibilities with her political career.
Mrs Mensch married Peter Mensch, the US-based manager of rock band Metallica, last year and she is moving with her three children to be with him.
Mrs Mensch won Corby at the 2010 election with a 3.4% swing from Labour to unseat former health minister Phil Hope.
The by-election is expected to be held on 15 November, the same day as elections for police and crime commissioners are held across England and Wales.