Last week's long-awaited speech laid out a long and complex process that is likely to drag on for five years, complicating if not poisoning Britain's frayed relations with its EU partners.
Cameron envisaged a general election in 2015, with the referendum pledge as part of the campaign platform. If he wins the election, Cameron will launch enabling legislation in Parliament and begin negotiations with the 27 EU member states for an amended British relationship with Europe. If the deal is satisfactory, and it remains almost completely undefined, Cameron will then fight for a "Yes" vote in the referendum in 2017.
Well, as the old French cookery books used to say, first catch your hare. With the British economy teetering on the edge of a triple-dip into recession, Cameron's chances of winning the election in 2015 are very uncertain. If he is forced once again to seek a majority in coalition with the Liberal-Democrats, as he is today, their devotion to the European cause may bring problems.
Secondly, nobody knows what changes are coming in EU governance. The members of the eurozone are inching toward a more federal structure in economic and fiscal policies, which may or may not translate into a more federal Europe in general. Nor do we know the fate of the euro itself.
The current conventional wisdom is that the euro crisis is virtually over, because the European Central Bank President Mario Draghi has pledged to buy whatever sovereign bonds are needed to keep euro members solvent.
This conventional wisdom is flawed, not least because the latest domino to look like falling is Cyprus, whose banks are in dire straits. Other EU members are balking at a bailout because so many of the Cyprus bank deposits come from more or less savory Russian depositors. Few European taxpayers relish the thought of saving the bacon of the Russian mafia or oligarchs.
The German and wider eurozone economies are stalled. Spain is in the grip of a political crisis fueled by scandal over the finances of political parties, millions of whose funds have just been found in private Swiss bank accounts. Italy faces a difficult election that may well sink the reform plans of the current technocratic and pro-European Prime Minister Mario Monti.
It may thus be conventional politics, rather than a sovereign debt crisis that determines the euro's fate. And last week, a new banking crisis with difficult implications for the euro and the ECB suddenly emerged. Italy's oldest and third-largest bank, Monte dei Paschi di Siena, revealed hundreds of millions in loses on hitherto-concealed derivatives at a time when it was supposedly being supervised by Draghi, as Italy's central banker.
The euro crisis is certainly not over, just morphing into different forms at a time when the European economy as a whole is showing alarmingly few signs of growth.
And then there is the German problem. The result of last week's state election in Lower Saxony was very grim for Chancellor Angela Merkel and cast serious doubt on her hopes of remaining in office in the general election this fall. She may be the most popular and respected politician in Germany but she now looks vulnerable to a coalition of Greens and Social Democrats. Moreover, the defeat of her party in Lower Saxony means her opponents now command a majority in the Bundestag, the upper house of Parliament.
In his speech, Cameron noted that the European Union is changing, thanks to the euro crisis and the shifts in the global economy, and that Britain's relationship was entitled to change with it. As this column recommended last week, Cameron laid down a forward-looking and bold vision for the new Europe: more competitive, with a more open economy, and seeking to comfort disaffected European voters by restoring more powers to national parliaments.
Merkel's response to the speech was to say compromises were indeed possible and French President Francois Hollande made it clear he wanted Britain to remain an EU member state. Less senior politicians complained that Britain couldn't change the EU rules from soccer to rugby nor start cherry-picking among EU responsibilities. And the response was cool even from governments like the Dutch, Danes and Swedes, who are philosophically inclined to Britain's reform plans.
But Cameron's speech has had a less hostile response than expected, with German legislators agreeing to his call for a more competitive Europe. Cameron's firm declaration to be a pro-European rather than a skeptic should be helpful -- except among diehards in his own party.
But five years is a long time in politics and an even longer time in the current confused but troubled state of Europe's economies and its politics. Cameron has five years to strengthen his arguments, to open debates in other European capitals and to win allies.
He will need them. If this were poker, Cameron is holding no more than a decent pair after the first three cards have been dealt, with two more unknown cards to come. Britain has faced tougher odds.