Labour activists insist they are still confident of winning the Oxford West and Abingdon constituency.
The party is launching a leaflet depiciting the Liberal Democrat emblem as a "crying canary" that seeks to dupe the electorate into voting for the party when voters actually want a Labour MP.
Labour claim that tactical voting for Dr Evan Harris, who won the seat for the Lib Dems in 1997, has slumped, and that only a vote for candidate Gill Kirk can keep out Tory Ed Matts.
Mrs Kirk said: "The Lib Dems only won here in 1997 courtesy of Labour supporters desperate to oust the Tory government.
"Things have changed dramatically since then and people intend to vote locally for the Labour MP and second-term Labour government they want. The Lib Dems are trying to scare people into voting tactically by suggesting that Labour can't win. That's nonsense.
Mrs Kirk denied a claim in a Lib Dem newsletter that she did not know the area. She said she had only recently moved from Oxford to London.
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