David Cameron has said in the past that he intends to campaign to remain in the EU provided that he achieves a satisfactory deal before the referendum. I've just realised he must be bluffing.
The reason for this is Number 10's announcement that EU citizens won't be able to vote in the referendum. They didn't have to announce this yet, so they're clearly trying to shut down debate on this topic quickly -- which again means they must be desperate to achieve this. It would have been much easier simply to let everybody discuss the pros and cons of different franchises, but then the outcome might not have been what they wanted.
And let's face it: There can be only one reason to be desperate to prevent EU citizens from voting in the referendum, and that's to achieve a vote in favour of Brexit, given that they're the only group of people living here who would be almost guaranteed to vote in favour of continued EU membership. It's worth noting in this connexion that the Tories have also ruled out giving 16- and 17-year-olds the vote -- another group that are likely to be more positive towards the EU than the average UK voter -- while being perfectly happy to let Commonwealth citizens vote, although they're likely to more lukewarm towards EU membership.
If David Cameron really thought he would be likely to campaign in favour of remaining in the EU, it would be nonsensical to move fast to ensure the EU's biggest fans are disenfranchised.
My guess is he's already expecting his negotiations will fail (if for no other reason because he's asking for things that any EU expert will tell him the other countries won't give him), and he'll then go out and say something along these lines: "I really wanted to remain in a reformed EU, but the other countries have turned their backs on us, so I will with a heavy heart have to recommend that this great nation leaves the EU."
Why is Cameron doing this? My guess is it's to save the Conservative party. If he came out in favour of leaving the EU already, some pro-business Tories would break out, and if he campaigned in favour of EU membership, a very large number of MPs would rebel. By pretending to negotiate in good faith, he keeps the pro-EU Tories happy, and by setting the negotiations up to fail, he ensures the Eurosceptics will eventually be happy.