Toby Young in the Telegraph today argues:
On the face of it, the case for a snap election is quite compelling... polling evidence suggests that Labour is making some headway... When the cuts start to bite in April and public sector pay is frozen, the government’s approval ratings will start to plummet. The Lib Dems are proving increasingly unreliable partners and Nick Clegg may have difficulty persuading his Parliamentary Party to continue to support the government if the AV referendum returns a “no” vote on May 1st. Wouldn’t it be better for Cameron to go to the country at a time of his choosing rather than be forced to go at a later date by the collapse of the Coalition when the auguries are less favourable?
Though he concludes that the case against an election is more compelling (it boils down to 'a bird in the hand is worth two in the bush').
Toby Young however makes this stupid mistake:
If he doesn’t call a snap election, he’s locked in for the forseeable... the Bill ensuring that Parliament can’t be dissolved unless 55% of MPs vote for a dissolution will receive Royal assent later this year. That means the Lib Dems will be able to prevent Cameron going to the country – and they surely will while their poll numbers remain in the toilet.
Of course Cameron can still call a dissolution of Parliament following the rule change. The Labour Party will always vote for an election, so the Lib Dems can not prevent it, but the Tories still can. It's basic maths.
Tory + Labour = 305+235 = 83% for dissolution
Lib Dem + all non-Tory votes combined = 650-305 = 53% for dissolution
The original 55% cut-off was set out on this basis. Obviously.
ETA - And matgb reminds me that the vote required for dissolution gone up to 66%, which better protects Cameron against rebellion among his own ranks, further weakening the Lib Dems, but in no way hampering him if he wants to call an election. Actually I think this shows how scared of his own backbenchers Cameron is.
My conclusion is - he would be reckless to call an election now. He can call one at any time in the next 5 years. However, I don't think there will be any good time for him.