Marine Le Pen has been accused of using “fake news” during a head-to-head debate with Emmanuel Macron days before the final vote of France’s presidential election, after she alluded to allegations circulating online that her rival has an offshore account in the Bahamas.

Mr Macron filed a legal complaint on Thursday, prompting the Paris prosecutor's office to open a formal investigation into whether falsified documents and false online news were being used to influence voting ahead of Sunday's second round ballot.

The Front National candidate, who has been urged by her father and predecessor as party leader to adopt a “Trump-style” campaign, asked Mr Macron if the online rumours about his personal finances were true during a virulent exchange watched by 15 million people.

The allegations, which appear to have originated on a right-wing website in the US, dominated the penultimate day of what has become an acrimonious election.

Ms Le Pen was met with a hostile reception when she made one of her last campaign stops to the Brittany region. French TV footage appeared to show her being hit with an egg thrown by protesters shouting “out with fascists” as she arrived at a logistics company in Dol-de-Bretagne.

And it was no easier going for the centrist candidate, who was met with booing and chants from disgruntled workers and union officials on a visit to a glass factory in Albi, near Toulouse. Mr Macron spoke to them for around 15 minutes, appearing to restore some calm. One union leader, Michel Parraud, called him “very kind and very polite” – but added he still didn't think a Macron presidency would do much for factory workers.

Late in the day, the former US President Barack Obama gave Mr Macron his support in a dramatic late intervention. In a video message, Mr Obama said he was endorsing the centrist “because of how important this election is”, to Europe and France and “the values that we care so much about”.

But it was the allegations about the former investment banker's finances from Wednesday night’s proceedings that dominated most of the election coverage.

Asked on BFM TV on Thursday morning if she had any proof to justify repeating the claims, Ms Le Pen admitted she did not.

She said she was not formally accusing Mr Macron of any wrongdoing. “Not at all,” she said. “If I wanted to do so I would have done it yesterday. I’ve just asked him the question. If I had proof, I would have claimed it yesterday.”

Speaking on French radio France Inter, Mr Macron denied the accusations and said he did not have any account in the Bahamas or any other tax haven. His team said the former investment banker was the victim of a “cyber misinformation campaign”.

The original source of the claims remains unclear. There have been various reports citing intelligence sources as saying Russia is targeting Mr Macron in a campaign conducted online. Disobedient Media, which was founded in California by the right-wing journalist William Craddick, attributed the claims to “leaked documents” when it first reported them on Wednesday afternoon.

Nicolas Vanderbiest, a commentator for France Culture, tweeted: “So the fake news story on Macron’s account in the Bahamas, we can say without being misleading, that it was by the Russians.”

Le Monde, a French newspaper debunked 19 things Ms Le Pen said during the debate that were untrue and two for Mr Macron.

“It appears clear that if Mr Macron was not always [showing] total respect for the facts, Ms Le Pen made a lot of approximations and falsehoods,” writes the newspaper.

An ardent critic of the EU, Ms Le Pen claimed the UK economy was better off since the Brexit referendum.

“The UK economy has never been better off since people decided to take back their liberty,” she said.

French Presidential Election Show all 20 1 /20 French Presidential Election French Presidential Election Voters line up to cast their ballots REUTERS French Presidential Election French expats queue along the street outside the Lycee Francais Charles de Gaulle to cast their vote in a polling station inside the school, in the first round of the 2017 French presidential election, in London, Britain April 23, 2017. REUTERS/Luke MacGregor - RTS13JM5 REUTERS French Presidential Election People line up to vote in the first round of 2017 French presidential election at a polling station in Vaulx-en-Velin near Lyon, France, April 23, 2017. REUTERS/Emmanuel Foudrot - RTS13HSP REUTERS French Presidential Election Police patrol polling stations in France REUTERS French Presidential Election Francois Fillon (L), member of the Republicans political party and 2017 French presidential election candidate of the French centre-right, casts his vote in the first round of 2017 French presidential election in Paris, France, April 23, 2017. REUTERS/Christophe Archambault/Pool - RTS13IH0 REUTERS French Presidential Election Benoit Hamon (C), French Socialist party 2017 presidential candidate, is surrounded by photographers as he leaves a polling station after voting in the first round of 2017 French presidential election in Trappes, near Paris, France, April 23, 2017. REUTERS/Vincent Kessler - RTS13I0Y REUTERS French Presidential Election French President Francois Hollande collects voting slips before casting his ballot in the first round of the 2017 French presidential election at a polling station in Tulle, France, on April 23, 2017. REUTERS/Georges Gobet/Pool - RTS13ITO REUTERS French Presidential Election A policeman walks by election posters near a polling station during the first round of 2017 French presidential election in Paris, France, April 23, 2017. REUTERS/Christian Hartmann - RTS13I3A REUTERS French Presidential Election Emmanuel Macron and wife Brigitte Trogneux REUTERS French Presidential Election Emmanuel Macron casts his ballot REUTERS French Presidential Election Emmanuel Macron, head of the political movement En Marche !, or Onwards !, and candidate for the 2017 French presidential election, waves hand during in the first round of 2017 French presidential election at a polling station in Le Touquet, northern France, April 23, 2017. REUTERS/Benoit Tessier - RTS13ICH SAA/ French Presidential Election Jean-Luc Melenchon, candidate of the French far-left Parti de Gauche and candidate for the French 2017 presidential election, leaves a polling booth in the first round of 2017 French presidential election at a polling station in Paris, France, April 23, 2017. REUTERS/Stephane Mahe - RTS13IKB REUTERS French Presidential Election Front National leader Marine Le Pen casts her ballot Marine Le Pen (L), French National Front (FN) political party leader and candidate for French 2017 presidential election, casts her ballot in the first round of 2017 French presidential election at a polling station in Henin-Beaumont, northern France, April 23, 2017. At R, Mayor of Henin-Beaumont Steeve Briois. REUTERS/Charles Platiau - RTS13IEI REUTERS French Presidential Election Early ballots are read as results continue to come in Reuters French Presidential Election Macron supporters react as results come in early in the evening AP French Presidential Election Supporters of Front National leader Marine Le Pen cheer as early results come in Reuters French Presidential Election Alamy Live News. J21KYW Paris, France. 23rd April 2017. Marcon supporters wave French and EU flags after the announcement that he is the leader in the exit polls after the polling stations have been closed. Supporters of Emmanuel Macron, the Presidential candidate from the social liberal political party En Marche! celebrate the exit polls, that see him in first place, ahead of Marine Le Pen from the Front National in the first round of the French Presidential election. Credit: Michael Debets/Alamy Live News This is an Alamy Live News image and may not be part of your current Alamy deal . If you are unsure, please contact our sales team to check. Alamy French Presidential Election Front National leader Marine Le Pen takes to the stage to address her supporters as fans cheer Reuters French Presidential Election Emmanuel Macron greets supporters on Sunday night AP French Presidential Election Emmanuel Macron and wife Brigitte Trogneux celebrate the incoming results EPA

The UK economy grew more rapidly than most analysts expected in the wake of last June’s Brexit vote and avoided a recession. However, the pound slumped to a 31-year low against the dollar on the night of the vote and inflation is now shooting upwards to 3 per cent as a result. In the first quarter of 2017 the rate of quarterly UK GDP growth more than halved on the previous three months to just 0.3 per cent amid multiplying signs of previously buoyant UK consumers beginning to flag.

Ms Le Pen also claimed the euro currency was circulating before 1999 and that the EU was costing France €9bn a year, statements which Le Monde said are both untrue.

Late on Thursday, Ms Le Pen’s team made its own complaints about the activity of hackers, claiming an online activist had confessed to repeatedly targeting and temporarily disabling far-right candidate’s website.