The next Liberal Democrat election manifesto will spell out the party's red lines for any coalition negotiations, Nick Clegg is to indicate today.
The Deputy Prime Minister will paint the document as a starting point for talks with political rivals, warning activists that they should not expect to implement everything in it.
A senior aide said the manifesto - being drawn up by Cabinet Office minister David Laws - would set out the things Lib Dems would "die in a ditch" to deliver.
However, they declined to say what policies would be regarded as "red lines", saying the process was in the "very early stages" and no decisions had been taken.
The prospectus will clearly show the commitments that the Lib Dems would "die in a ditch" to keep in a power-sharing deal.
Clegg is to give details of his approach in a speech to the party's annual local government conference in Manchester.
While admitting that the Lib Dems have taken a "hit" as a result of entering coalition with the Tories, he will caution against "hankering for the comfort blanket of opposition".
Being a party of government means there will be far greater scrutiny of policies during the 2015 campaign, and the Lib Dems will need to present more of a "strong, sharp identity" than before.
"The idea that in a general election we can be under a national spotlight and yet run the campaign as a series of loosely linked by-elections simply isn't possible," Mr Clegg will say.
"We can be singing different verses - but they must all be from the same song."
The Lib Dem leader will insist it was right that the party's last manifesto highlighted four key priorities - raising the income tax threshold, the pupil premium, economic rebalancing and political reform.
But he will admit the pledge to oppose tuition fee rises was a "mistake", and promise that next time there will be a clear distinction between "commitments" and "ambitions".
"I want the manifesto to set out our ambitious vision for a liberal society but it must be a to-do list, not a flight of fancy," Mr Clegg is to say.
"That doesn't mean 'pre-negotiating' our manifesto - producing a bland, generic set of plans we know either of the other parties could sign up to. Far from it.
"We can and must fight the next election on a platform of distinct, forward-looking, liberal policies...
"But, building on the approach we took in 2010, we will be even clearer with people about the commitments which are priorities, and the ambitions which we accept may be affected by resources and circumstances."