* Ferrand under investigation in financial impropriety case
* Leader of parliament's lower house denies wrongdoing
* Ferrand maintains Macron's confidence - govt spokeswoman (Recasts, adds government spokeswoman)
By Elizabeth Pineau and Caroline Pailliez
PARIS, Sept 12 (Reuters) - French National Assembly President Richard Ferrand was determined to stay in his job after investigating judges placed the close ally of President Emmanuel Macron under formal investigation in a financial impropriety case, his office said.
Judges in the northern city of Lille questioned Ferrand all day Wednesday in a case that could bring renewed scrutiny to Macron's promise to clean up French politics.
Ferrand's office said he denied any wrongdoing, adding he would use the investigation to defend himself and was confident the case would be dropped.
"The president of the National Assembly is determined to continue with the task conferred on him by his political family and his voters," it said in the overnight statement
Ferrand maintained Macron's support, government spokeswoman Sibeth Ndiaye said.
"Richard Ferrand is innocent until it is proven otherwise," Ndiaye told Europe 1 radio. "It is logical that the president retains his confidence in Ferrand because he is a loyal man, who has had, I believe, an exemplary political career."
Under French law, being put under formal investigation means there is "serious or consistent evidence" that points to probable involvement of a suspect in a crime.
It is a step towards a trial, but many investigations have been dropped without going to court.
A previous investigation by French public prosecutors into Ferrand's financial dealings was dropped in late 2017. Ferrand resigned as a minister during that probe.
As a lawmaker, he now heads Macron's ruling party in the lower house of parliament. The latest probe relates, like the previous one, to Ferrand's management of a health insurance company in Brittany.
The new investigation was launched after the anti-corruption group Anticor refiled its original complaint in a different jurisdiction, an aide to Ferrand said.
His office said Ferrand was confident the case would be closed because no new evidence had been put forward since it was dropped the first time.
Macron's right-hand man during the 2017 presidential campaign, Ferrand became embroiled in allegations of financial impropriety within days of Macron's victory in May.
The allegations that Ferrand allegedly benefited improperly from property deals done eight years ago by a health insurance fund he managed tainted the early weeks of the Macron presidency. (Additional reporting by Leigh Thomas; Writing by Leigh Thomas and Richard Lough; Editing by Himani Sarkar, Paul Tait and Michael Perry)
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