The document, found after last week’s first debate, reveals the Lib Dem leader was coached to adopt David Cameron's style.
The document includes notes such as: "DC (David Cameron) talks a lot in the language of values. We need to do this." It also advises Nick Clegg to 'speak more clearly' and 'appear relaxed'.
The dossier was found in the back of a cab on Thursday 15th April at about 10.30pm, soon after the end of the first election debate.
The driver, who was driving the unnamed Lib Dem staff from Parliament, said: "It's extraordinary that someone like him could just leave this stuff in a taxi. It's very sloppy to say the least and I thought people should know.”
The dossier was written by John Sharkey, chairman of the Lib Dem election campaign team and Mr Clegg's strategic communications adviser. Mr Sharkey repeatedly coaches Clegg to appear ‘normal’, and to distance himself from Gordon Brown.
Further advice included ‘standing back from his Labour and Tory rivals’ and ‘saying yes to a deal in a hung Parliament if party policies and values are put into practice’.
The dossier reveals that Lord Rennard was heavily involved in planning the Lib Dem manifesto launch, despite resigning as the party's chief executive last year following a row over his expenses.
Last night a spokeswoman for Mr Clegg said of the dossier: "It is private property and we'd like it back, please."