PARIS (Reuters) - A senior Socialist minister said on Tuesday he might back centrist Emmanuel Macron in France’s presidential election, a new blow to the left’s hopes that could help Macron as he battles to maintain his campaign’s momentum.

Emmanuel Macron, head of the political movement En Marche !, or Forward !, and candidate for the 2017 French presidential election, attends a political rally in Toulon, France February 18, 2017. REUTERS/Jean-Paul Pelissier

The pronouncement by agriculture minister and government spokesman Stephane Le Foll came as opinion polls pictured a wide multi-candidate race, in which far-right leader Marine Le Pen was holding onto recent gains, keeping debt and foreign exchange markets on edge.

Two polls showed ex-banker Macron neck-and-neck with conservative rival Francois Fillon as favorite.

A third, from Elabe, had Macron in retreat, and made former prime minister Fillon of The Republicans favorite for the first time since a scandal over alleged fake work rocked his campaign four weeks ago.

All recent polls show Le Pen ahead in the April 23 first round, but losing a May 7 run-off to whichever of Macron or Fillon topped round one.

They also show, however, that her losing margin has shrunk in to as little as 6 percentage points from more than 10.

Le Foll’s potential defection is the latest in a slew of bad news for France’s divided political left.

“I support the man who has been chosen (by the Socialists), but the moment comes for political responsibility with regard to what is at play, with regard to Marine Le Pen and with regard also to the program of Francois Fillon,” he said on BFM TV.

Asked whether this meant he would back whoever was best placed to prevent a Le Pen-Fillon runoff, he said: “Exactly!”

Foreign Minister Jean-Marc Ayrault has also said he might back Macron - rather than the ruling Socialists’ chosen candidate Benoit Hamon, who is a distant fourth in the polls.

Despite the prospect of heavyweight Socialist backing, the polls show Macron’s campaign losing momentum.

Elabe pollsters reckon he has made a series of mis-steps that explain how they now see Fillon ahead.

“He has had 10 difficult days,” they said.

LEFT DIVIDED

Macron angered opponents on the right during a visit to Algeria last week by calling France’s colonial past a crime against humanity. He has upset pro-gay marriage supporters by saying their opponents had been humiliated by the government when it pushed through the gay marriage bill in 2013.

On Tuesday, Macron took his centrist and pro-European campaign to London, home to a large expatriate French community who get to vote in the elections.

The anti-immigration, anti-European Union Le Pen, meanwhile, caused controversy on a trip to Lebanon where her plans to meet a senior Muslim figure were canceled after her refusal to wear a headscarf.

Le Pen’s surge has worried investors concerned that her policies will further destabilize fragile European unity, blow apart the euro zone and hurt the value of French debt.

The cost of insuring French government debt against default has risen to its highest level in more than three years and sterling rose almost 1 percent against the euro to its highest in two months.

Fillon, meanwhile, was tweaking the healthcare policies that caused a campaign wobble earlier this year, having apparently put allegations his wife Penelope was paid hundreds of thousands of euros for work she may not have done behind him.

Fillon has said the work was genuine. An official inquiry is under way.

Besides the three-way fight, discussions to unite candidates on the left looked to be going nowhere.

Hamon is pushing a hard-left program that divides his party and competes for votes with another leftist, Communist-backed Jean-Luc Melenchon.

Melenchon is in fifth place, but a combined Hamon-Melenchon vote could theoretically put them into first or second and therefore into the run-off, instead of Fillon or Macron, against Le Pen.

Talks between Melenchon, a veteran campaigner, and Hamon, an ex-education minister, were tentative from the start and both have acknowledged wide policy differences.

Hamon gave the latest indication on Tuesday that they were unlikely to be joining forces.

“There is a desire on Melenchon’s part to go on right to the end,” Hamon said on Europe 1 radio. “I respect that...In any case, I will work on right to the end.”

Political analysts are also eying an imminent decision from veteran centrist Francois Bayrou on whether to stand. If he stands, that could hurt Macron, but backing from Bayrou could be a further boost.