President Jacques Chirac of France was under pressure on Sunday night to get more involved in campaigning for a Yes vote in May's referendum on the European constitution as a second opinion poll in a week showed hardening public opposition to the treaty.

In a poll to be published in Le Figaro on Monday, 52 per cent of those who said they planned to vote in the referendum on May 29 are against the treaty, compared with 40 per cent in early March. The poll, conducted by Ipsos on Friday and Saturday, follows a poll by Le Parisien published on Friday showing for the first time a majority against the constitution.