His slump only ended when centrist François Bayrou confirmed he would not run for president and backed Mr Macron.

Since then, he has consolidated support, winning the backing of Socialist former Paris mayor Bertrand Delanoë who called him "a reformist, a European and a realist" best-placed to beat Ms Le Pen.

According to Le Figaro, a significant group of Socialist progressives, including government ministers, are about to publicly back Mr Macron. Their decision to drop the official Socialist candidate Benoit Hamon could pose problems, however, for a candidate who has promised not to do deals with any political camp.

Mr Macron's rivals insist that far from offering change, he is the natural heir to President François Hollande.

The new polls were released as Mr Fillon sought to build new campaign momentum after seeing off a challenge to oust him as party nominee. This culminated in a mass rally in Paris on Sunday and a decision on Monday by Right-wingers to close ranks behind the ex-prime minister, who could be placed under formal investigation for corruption next week.