After Chris Huhne's resignation a by-election will be held in his constituency of Eastleigh.
A source close to Labour leader Ed Miliband signalled the party's determination to fight for the seat:
We recognise this is an uphill struggle, but as a one-nation party we fight in every seat and campaign in every part of the country.
We intend to campaign hard against both coalition parties.
It is understood that Eastleigh is 258th on Labour's target list.
The Liberal Democrat leader of Eastleigh Borough Council, Keith House, he was "very sad" about Huhne's resignation, saying he had been a "hard-working MP".
The Liberal Democrats have a solid base in Eastleigh. They have won every election here for eight years and we will go forward
The Tory candidate is likely to be business consultant Maria Hutchings, 51, who famously assailed Tony Blair over care and education for her autistic son during the 2005 general election campaign.
A local party source said:
Maria is popular in the local party and has already been campaigning in Eastleigh.