Left-wing singer Billy Bragg is urging Labour and Lib Dem voters in three hotly-contested seats in Dorset to vote tactically on polling day.
Mr Bragg backed tactical voting during the 2001 election
Mr Bragg is calling for Lib Dems in Dorset South to vote for Labour and Labour supporters in Dorset West and Dorset Mid & Poole North to go Lib Dem.
A spokesman for the Conservatives dismissed the move as simply a "stunt".
Labour said people could vote for them "with confidence". The Lib Dems said they wanted as many votes as possible.
Mr Letwin currently has a 1,414 majority
Mr Bragg, who is also resurrecting his 2001 vote-swapping website, said he would be voting for the Lib Dems in his own constituency of Dorset West, where Conservative Oliver Letwin is the current MP.
"However, that won't make much difference if the Tories take back the highly marginal seats of South Dorset from Labour and Mid-Dorset from the Lib-Dems," he said.
A spokesman for the Conservative party in Dorset said: "He did the same stunt last time and Oliver Letwin remained our MP and an excellent MP.
"It is quite clear that the tactical voting that was around in 1997 is falling apart and if anything we might even be seeing tactical voting against Mr Blair."
A spokesman for the Labour party in the South West said: "The Labour party has in Jim Knight a fantastic MP and candidate for South Dorset.
"We also have fine candidates contesting difficult seats nearby. People can vote with confidence should they choose to across the county."
A spokesman for the Lib Dems said: "Our stand on this is that we obviously want as many people to vote Liberal Democrat as possible in all seats but the electorate is increasingly sophisticated and people have to decide whether they want to use their vote in that way."