Yes I possibly am being optimistic, or indeed naive to think that a Government Minister would keep his word, given that he didn't before. And I take your point that he didn't quite say that the levy would end after 2015. And he didn't quite say that it wouldn't.
In my view, if you have to hide behind verbal sleight of hand and cunning word-play like this, rather than being open and direct, it says a lot about your character.
He was asked if the levy was going to be continued indefinitely. That's a fairly straight question. He replied by saying that he had no plans to change it, thus slithering away from giving the straight answer it deserved.