Here's the likely Conservative narrative:
biggest share of the vote + largest number of seats + Clegg definition of moral mandate to govern = Cameron in Number 10
The first two inputs are right. The Clegg factor is debatable.*
But there's something wrong with the bigger picture. The Conservatives say they like the present electoral system. They accept the constitutional arrangements whereby the sitting Prime Minister has the right to try to form a government in the event of a hung parliament.
In the event of a workable Lib/Lab deal the Tories can stamp their feet and cry unfairness. But wouldn't it be hot air and hypocrisy?
* UPDATE 10.43AM Clegg has just reaffirmed his definition of the moral mandate to govern. Ball in the Tories' court. Looks like Lib Dems have surrendered their leverage for voting reform.