MR - the change in the system to fixed term parliaments, with some provisions for an early election offer a completely different scenario than before.
Prior to the law being enacted, it was within the Governments gift to declare an election, presumably when the polls favoured them. So the incumbent always had an advantage. The only way the opposition could force an early general election was by forcing through a vote of no confidence.
Now, should a government wish to take advantage of favourable polls, they have to call a vote, and get that vote through, given plenty of warning about when an election could occur.
Thats a big diference.....