Now that the Lisbon treaty has been approved by Irish voters it will probably be in force by the time of the next election. I was hoping that it would be best of three with a third referendum to decide who wins but apparently "yes means yes" but "no means try again".
A referendum after it is in force would be a de facto in or out vote and it is unlikely that David Cameron will want that because it will aggravate splits in the party and he would probably lose which would damage both him and Euroscepticism.
However doing nothing in response would make his current statements about "not letting it rest" look laughable, which will also annoy the party and make him look weak. So he needs to do something to satisfy Eurosceptics in the party and the country.
What I would do in his shoes would be to offer a referendum on the following question- "Should future European Union treaties require majority support in a referendum in order to be ratified?".
This would put the brakes on any deeper EU integration without the consent of the voters & force Labour and the Lib Dems into the position of arguing against democracy.