The No camp in France's referendum on Europe's constitutional treaty stepped up its campaign over the weekend targeting every shade of the political spectrum in an attempt to consolidate its lead in the opinion polls.

The latest poll, published on Sunday by the Ifop institute, showed 52 per cent of people who have decided how to vote oppose the treaty. But the outcome of the vote on May 29 is still up in the air and much will depend on the final week of campaigning.