This is a stupid idea, because the prime minister of Britain is not directed by anyone other than his or her constituents. These are the only people who get to vote for the PM. Once the election is finished and the votes counted, the prime minister is the MP who can command the support.
During the morning's campaigning, Mr Cameron's key proposal was that anyone taking over as PM following the death, overthrow or resignation of the previous incumbent would have to call an election within six months.
A new PM would be free to request a dissolution at any time during the six-month period, which would allow time for him or her to appoint a ministerial team and set out a programme for government and for Parliament to deal with any outstanding business, under the plans.
"It means putting the people in charge, I believe you should be in Number 10 because people have voted for you," he said. (1)
Cameron seems to have confused this with the idea that the prime minster is some sort of directly elected president. it's quite frightening that one of the lead candidates for the job seems to have a complete misapprehension about what it actually is.
Cameron's floating this idea to try to distract people from the recent talk about more general constitutional reform - his party remain dead against proportional representation, so this is a token. It has the advantage of cashing in the vague, lingering resentment over Brown's assumption of power. It is stupid poster politics, but it might have some traction.
1 - "Unelected PMs must call poll within 6 months - Cameron," unattributed article. Published on the BBC website, 24th of April, 2010. (http://news.bbc.co.uk/2/hi/uk_news/politics/election_2010/8641552.stm)