If the Tories and New Labour are today cheeks of the same arse, then the Lib Dems are the thing in the middle.
Clegg’s party is straitjacketed by its own support base. Across much of rural England and in the small towns of the south, the Lib Dems are a catch-all anti-Tory Party. In the cities they often function as substitute Tories against Labour. If Clegg were to make a clear policy announcement or signal a choice of coalition partner he would lose half his party.
The goal of progressive voters is to prevent a Tory overall majority. Therefore, in those seats currently not held by the Tories but winnable by them, people should vote for the candidate best placed to defeat the Tory. In all other seats they should vote for the most progressive serious candidate, usually Labour or Green.