Ed Miliband is to vow to make unemployment a key battleground issue in a forthcoming by-election after Tory MP Louise Mensch announced her intention to quit the Commons.
The Labour Leader will pay a visit to 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 Corby seat in the forthcoming poll, 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 is expected to say: "People in Corby have seen long-term youth unemployment nearly double over the last year as a result of decisions made by an out-of- touch Government. That's why Labour will make unemployment in Corby one of the key issues in this by-election. I visited Corby a few weeks ago and people are crying out for a strong voice to represent them in the face of a recession made in Downing Street.
"Andy Sawford will champion Corby and campaign for the real change so we can build an economy that works for working people."
Labour's prospective parliamentary candidate, Mr Sawford, earlier said: "Labour is now looking forward to the campaign ahead, fighting for action on jobs and the economy, supporting our local services, which are facing massive cuts, and working with local community organisations."
In an email to Labour Party members, general secretary Iain McNicol warned that it was "an election we could lose", but stressed grassroots supporters would "mean the difference between winning and losing".
Mother-of-three Mrs Mensch announced on Monday her intention to leave Westminster and move to the United States with her family. The backbencher, who shot to prominence as a member of the Culture, Media and Sport Select Committee which investigated the phone-hacking scandal, said she was "devastated" but that it was a "necessary decision".
Mr Cameron said Mrs Mensch had been an "inspiring" MP and hinted that she had been in line for a role in the Government. But her husband, Peter Mensch, manager of rock band Metallica, lives in New York and she has been forced to divide her time between the UK and US.