The Prime Minister made it sound so straightforward this morning.
It won’t be, not least because there are now some in the councils of Europe who would be pretty sanguine about a ‘Brexit’, even happy that without London’s obstructionism the dream of a United States of Europe has a better chance of being realised.
David Cameron has set the ball rolling, but it is he who must produce something.
It is simply not an option to go to the British people in 2017 and say “Well, I asked for something, they gave me nothing, but let’s have a referendum anyway”.
His own party would be torn apart in such a scenario.
So what are his chances? If you woke up this morning in Paris you would think ‘none at all’.
Within minutes of the speech, France’s Foreign Minister Laurent Fabius produced the sound-bite of the day with, "If Britain wants to leave, we will roll out the red-carpet."
You get the feeling that every French minister has been itching to use this line ever since Cameron opened hostilities on French tax exiles last year.
Paris may be asking for British military help in its adventures in Mali, but the city is full of politicians who see the British as the last great obstacle to the completion of a centralised, technocratic ‘social’ europe in their own image.
Expect them to fight any concession to Cameron that might be interpreted as ‘Europe a la carte’.
- Watch: Tony Blair: Cameron's referendum pledge is "driven more by [the] internal Conservative party problem on Europe"
But in northern (and to a lesser degree eastern) Europe there have been much more sympathetic noises this morning, even if it would be an exaggeration to call them supportive.
The Dutch, the Swedes, the Finns, the Czechs have all expressed an interest in at least talking about the Cameron agenda.
And, unlike the French, when they say they value British membership of the EU, they don’t tend to follow it with the word "but".
In the battle between northern economic free-traders and southern dirigiste protectionists (a crude caricature, I know) they really value Britain’s negotiating strength.
But these days if you really want to know what is likely to happen, you have to go to Berlin.
This is where I started the day, and was struck by the concerted efforts being made by leading Germans not to dismiss Cameron out of hand.
Angela Merkel set the tone with the words "Europe must find a compromise that is fair to everyone."
The Germans know they are going to have to talk to Britain, and can see a clear advantage in getting Britain’s co-operation and acquiescence as the Eurozone integrates further.
There is a strong decentralising tradition in Germany, on both left and right, that is horrified at the prospect of an overweening central power in Brussels interfering in areas that even the Federal Government in Berlin is happy to leave to local politicians.
Peter Gauweller, a leading member of Merkel’s coalition allies, the CSU, even said this morning that “the British are the only sane ones in Europe.”
The danger for Cameron is over-playing his hand, which arguably he may have done already. Irritation at London’s antics is in danger of draining Berlin’s reservoir of goodwill.
The final reason for thinking that Cameron’s task may not be hopeless is that, in the near future, the architecture of Europe is going to have to change anyway.
The 17 members of the Eurozone are heading to a place that the other 10 (soon 11) are not going to follow.
Some may catch-up pretty quickly, others never will. Which means the formal recognition of a two-speed Europe is now both inevitable and desirable.
Those thinking about Europe’s future recognise this - even those doing their thinking in Paris.
Two Paris-based think-tanks, ‘Europa Nova’ and the ‘Jacques Delors Foundation’ - both impeccably integrationist - told me this week that it may be to everyone’s advantage to redefine the position of the Euro-Outs within the EU as a whole.
They imagine something along the lines of an enhanced European Economic Area whose members would be full members of the EU and the single market, but not part of the newly federalised Eurozone.
As an added advantage, if such a status existed for Britain, Denmark, Sweden, whoever, the likes of Norway, Switzerland and Iceland might want to join as well.
Such an outcome is a long way off, and may never happen, but it is most definitely being talked about.