Although I'm looking forward to his speech, I don't have high hopes. Daniel Hannan wrote a piece in defence of the PM last week:
At this stage, several of my regular commenters will say "Ah, but a referendum is worthless unless it takes place in this Parliament". Well, OK, chaps. If you have a way to make Labour and LibDem MPs vote for one, I'm all ears. But if you haven't, it's really a bit much to blame the Tories for how the other parties vote.
But we all know that Dave can't be trusted. If he's serious about a referendum, it would seem sensible to at least try for one ahead of the general election, as I noted in the comments:
Easy. Cameron says that he would like the referendum to take place in this parliament, he whips his party into supporting that, and he dares Labour and the Lib Dems to vote against. If they succeed in crushing the proposal, they look bad, and he can honestly say that he tried.