UK's EU future dependent on other member states

In his reaction, French foreign minister Laurent Fabius compared the EU to a football club: "Once you've signed up, you can't decide to start playing rugby."

His Swedish counterpart Carl Bildt tweeted that while Cameron's call for flexibility sounded "fine", a Europe of 28 speeds would be not be a Europe but "a mess."

But although Cameron's colleagues were quick to react - there was little of substance to react to. The British Prime Minister, who is trying to win over eurosceptics in his own party - promised an in/out referendum on EU membership by the end of 2017, provided he wins the next election.

The public poll would be after changes have been made to make the EU more open, flexible and democratic. "Nothing should be off the table" he said but did not elaborate much on what should be on it.

He referred several times to the importance of the single market and asked whether "expensive peripheral European institutions are justified", whether the commission can continue to get "ever larger" and why EU programmes that do not work are not shut down.

He also called for a greater role for national parliaments and asked whether the "balance is right" in EU law on the environment, social affairs and crime. His most specific charge was that an EU law on working hours meant British doctors were not allowed to work the hours they needed to.

Many reactions suggested he had opened a can-of-worms discussion on Europe simply for domestic politics reasons.

European parliament chief Martin Schulz said: "We have to focus on jobs and growth rather than getting lost in treaties discussions" while the leader of the parliament's liberals, Guy Verhofstadt, said Cameron was "playing with fire."

There were also some allusions to the likelihood that the British question would dominate EU affairs for the coming five years. Joseph Daul, leader of the parliament's centre-right, said Europe "cannot be taken hostage" until 2017.

The political reactions underline the difficulty Cameron is likely to have even getting to the stage of treaty negotiations which require a majority of member states to call a convention, the first legal step in treaty change.

The convention - a large assembly made up of national and European politicians, member states and the European Commission - would then have to agreed treaty change proposals. The convention's proposals would then go to member states for an 'intergovernmental conference.' Any resulting treaty changes would have to be agreed unanimously.

EU council president Herman Van Rompuy indicated recently that member states now favour using current treaties to make changes to stabilise the eurozone.

Summing up the general feeling among other member states, Irish Europe minister Linda Creighton said there is "no appetite whatsover" for treaty change.

If there is no treaty route, that would leave Cameron with trying to unilaterally negotiate the changes it wants with its EU partners.

Whether the EU arrives at this particular juncture is likely to depend on a complex trade off on how much other member states are prepared to meet London's demands and how big the swell of opinion in the UK is on leaving the EU altogether.