The report by the EU Scrutiny Committee gets to the heart of the problem facing David Cameron. He can, in all likelihood, secure a deal which touches on his four demands to some extent. This will enable him to show that the negotiation process has worked, and to settle a deal back home to stay in.

However, to get a bigger movement will require Treaty change and this cannot be delivered in the timescales promised for the referendum. There needs to be an agreement for Treaty change across the other 27 Member States and this might be possible. But it won't have been passed by everyone in time of the referendum. This is at least in part because a number would have to hold referendums themselves.

So a deal for the UK could include a promise of Treaty change but not to guarantee that it will be delivered.

This illustrates that the referendum issue is fundamentally down to the politics and how the deal is communicated. There is a part of the population that will always vote to stay in, and a part that will always vote to come out. David Cameron has to secure enough change that reassures the group in the middle, the undecideds, or those prepared to be convinced.