One of the first pieces of legislation passed by the coalition government was the move to fixed-term parliaments. Gone is the drama of the Prime Minister having to go to the Queen to ask her to dissolve parliament.
If David Cameron still had to call an election, he would be open to the same sort of criticism he gave out to Gordon Brown in the run up to 2010 election. Cameron could be described as weak, indecisive and running scared of the electorate.
There are practical issues too. The business of government almost grinds to a halt. The coalition have rushed though legislation that was expected to be controversial; trebling tuition fess, cutting welfare payments for the disabled, the bedroom tax and measures to privatise NHS services, all in the first three and a half years of the five year fixed-term parliament. This leads to situations such as earlier this week when there was no ministerial statement at all until the Speaker called a Minister to the House after Labour asked an urgent question about the American company Pfizer taking over the successful British drug development company Astra-Zenica.
The Coalition is limping towards the general election, its like Clegg and Cameron are locked together in a three legged race to 2015 trying desperately not trip each other up. They could do honourable thing and repeal the 2010 fixed term parliament act and call an election but they won't, they are clinging to power but at the same time not doing very much with it.