In the Bloomberg speech of 2013 in which he promised a referendum on British EU membership by the end of 2017, David Cameron promised to carry out ‘renegotiations for fundamental change’ of Britain’s terms and conditions of their EU membership. In a speech at Chatham House today, he spelt out in more detail precisely what this will entail. In so doing he confirmed what many already suspected. No such fundamental change is in prospect. Yet the renegotiation, whilst substantively somewhat pointless is politically profoundly necessary.

In substantive terms, the Prime Minister has already achieved much of what he wants. The European Commission has cut back on red tape and is putting forward legislation intended to make the EU more competitive (initiatives on a digital single market and capital markets union foremost among them). Indeed, if the government were not expending all its energy on a renegotiation, it might have well have got far more of what it wants by focussing it within the normal EU legislative system.

On the vexed question of ever closer union the Prime Minister has already secured – in June 2014 – a declaration by EU leaders that not all member states want to travel in the same direction at the same speed. The proposed ‘red card’ that national parliaments could wield against EU legislation is not that different form the current ‘yellow card’ and would encounter the same problems when it comes to the willingness and ability of national parliaments to make use of it.

As for British fears regarding the possibility of the EU coming to be dominated by Eurozone members, there are certainly grounds for concern. And, guarantees about the integrity of the single market and mechanisms to prevent discrimination against non euro members will become crucial issues if the Eurozone integrates further. Yet surely such a debate should wait until such integration is in prospect? After all, this would require treaty change, and Britain could secure its desiderata at that point or threaten veto the whole show.

Finally, the most problematic area spelled out in the PM’s speech was his demand that limits be placed on the access EU migrants in the EU enjoy to benefits. David Cameron again underlined that people coming to Britain from the EU ‘must live here and contribute for four years before they qualify for in work benefits.’ Most EU lawyers, however, agree that this cannot be done without breaching the EU’s constitutionally enshrined principle of free movement of labour. The only alternative would be treaty change which is simply not doable before the end of 2017.

Interestingly however, in the letter to European Council President Donald Tusk that was sent immediately after his speech, the Prime Minister provides himself with slightly more wiggle room.

He argues that there is a need to find ways of reducing the numbers of people coming to the UK, indicating that limiting in work benefits might be one mechanism by which to achieve this. It becomes, therefore, an option to achieve a certain end, rather than an end in its own right.

So British demands have already been met, or are not of real significance yet, or are being fudged to appear as if they have been met. The difference between the public agenda and the formal demands on immigration provides a clue as to what is going on here. The substance is really not the point. The major purpose of the renegotiation has never been a ‘new settlement.’ Rather, it is to keep the Conservative Party in parliament onside.

David Cameron needs to convince his backbenchers that he has reformed the Union. Research by the think tank Open Europe has suggested that 203 of the 330 Conservative MPs can be characterised as ‘swing voters.’ That is to say, they are either not particularly interested in the EU or who are waiting until the results of the renegotiation before making up their minds on the referendum.

It is this constituency at whom the renegotiation is primarily targeted, and for three reasons. First, no Prime Minister, particularly not one with a slim majority, wants a bunch of rebellious back benchers on his hands.

Second, and more significantly, David Cameron has stated that he will not stand for re-election in 2020, leaving the way open for a succession battle. Should sufficient numbers of Conservative MPs prove dissatisfied with what he gets from Brussels, this could lay the way open for a putative leader to emerge as leader of the Conservative ‘leave’ camp. Sufficient parliamentary support would ensure this candidate got through to the second round of a leadership contest in which the largely Eurosceptic party membership would decide the outcome. Both Boris Johnson and Theresa May have been widely reported to be considering this course of action.

And – third –  the way the parliamentary party breaks over Europe will have a bearing on the outcome of the referendum itself. One reason why the ‘in’ camp managed to triumph so comfortably in the 1975 referendum was that the whole political mainstream was arrayed under its banner. On the out side were to be found figures widely seen as extremists, such as Tony Benn and Enoch Powell.

A similar constellation of forces would favour the ‘remainers’ when the next popular vote on EU membership is held. In contrast, the presence of a big Tory beast at the head of the ‘leave’ camp could shift the balance. Initial research has suggested that leadership will have an impact on the outcome of the referendum: Cameron supporting ‘Remain’ may move the result by 2%. Corbyn’s endorsement of ‘Remain’ increases support for that side by 2.8%. Indirectly, therefore, the renegotiation is crucial for the referendum itself.

David Cameron’s negotiations with Brussels, then, will be as crucial politically as they are minimal substantively. The ultimate test of their success will be found in Westminster not Brussels.

This column was first published by The UK in a Changing Europe