France's presidential election campaign lurched deeper into uncertainty on Tuesday after centrist Emmanuel Macron was forced to deny an extramarital affair while financial scandal continued to dog conservative rival Francois Fillon and his party.

Macron has become favourite to win by a thin margin since a scandal two weeks ago surrounding the work of Fillon's wife, Penelope, knocked the former prime minister off the top spot.

Late on Monday, the centrist former economy minister and ex-banker sought to move his campaign on, taking an opportunity to dismiss rumours he had a relationship outside his marriage to Brigitte Trogneux.

Separately, a day after Fillon held a major news conference to re-invigorate his scandal-hit campaign, an opinion poll for Harris Interactive said 65 per cent of French people wanted him replaced as candidate of the centre-right.

In that press appearance, Fillon apologised for organising hundreds of thousands of euros in payment for his wife and family for carrying out work for him, but vowed to fight on as candidate.

Also on Tuesday, a judicial source said a magistrate had ordered another prominent member of Fillon's The Republicans party - ex-president Nicolas Sarkozy - to stand trial over irregularities - a poignant reminder of the party's past brushes with financial scandal.

Uncertainty about the outcome of the election, taking place in two rounds on April 23 and May 7, has this week driven the premium that investors demand for holding French over German government debt to its highest for almost four years.

Opinion polls show Macron ahead of Fillon in the first round of the election, but only by a few percentage points, and behind Marine Le Pen, leader of the far-right National Front.

Only the top two candidates go through to a second round on May 7. Polls show that Macron would beat Le Pen with about two thirds of the vote and that Fillon would win by a smaller, but still comfortable margin.

In its daily opinion poll update on Tuesday, pollster Opinionway left its first round score little changed from Monday, putting Le Pen on 25 per cent, Macron on 23, and Fillon on 20.

It raised its prediction for the Macron vote in the second round to 66 per cent from 65.

Source :Times Of Oman