Head of the French Socialists François Hollande, with EU parliamentary leader Martin Schultz at his side, has launched his party’s campaign to encourage the country to vote yes to the European Union Constitution. France’s referendum is due by late May or early June.Hollande said: “Our ‘yes’ must be clear; we are not making any confusion as to what it is about. For us, the sole subject of the consultation by referendum is the Constitutional Treaty; it is in no way Turkey or any other candidate for EU membership.” Hollande led a party poll to victory in December. The treaty — needed to make the enlarged EU work smoothly — must be ratified by all 25 EU members to come into force. Several countries will hold referendums on it.