Half a million people received duplicate polling cards in the post, which would allow them to cast two votes at the first round of the election, held on April 23.
French authorities confirmed they would not be investigating the potential electoral fraud until AFTER the election, when retrospective prosecution may take place.
This could crush Ms Le Pen’s dreams of surging to power, as most French nationals living outside of their country are not right wing – demonstrated by the fact many feel they depend on the European Union (EU) to guarantee their stay in foreign countries.
Marine Le Pen is facing wipe out in French election after a computer blunder
Emmanuel Macron visited London in February and held rousing talks urging London’s 300,000-strong community to vote for him.
London’s French population equates to France’s sixth largest city, and now many of those 300,000 people will have the chance to vote for Mr Macron twice.
Far left candidate Jean-Luc Melenchon, who has surged in the polls recently and threatens to break into the leadership race against Ms Le Pen and Mr Macron, could also benefit from this catastrophic error.
Half a million people received duplicate polling cards in the post
She said: “This year, this is the first time I have asked myself the question, would I take advantage of this anomaly to vote twice? My candidate was low enough in the polls.”
My candidate was low enough in the polls
Voting twice is a crime, but police will only find out if they run a check on the individual through their computer systems.
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The punishment can be up to two years in prison and a fine of about £13,500.
Things you didn't know about Marine Le Pen
Wed, April 5, 2017
Marine Le Pen is a French politician who is the president of the National Front, a national-conservative political party in France and one of its main political forces.
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Described as more democratic and republican than her nationalist father, she has led a movement of "de-demonization of the Front National" to detoxify it and soften its image
Emmanuel Macron with London Mayor Sadiq khan, after a visit to London urging ex-pats to vote for him
France’s Interior Ministry has said it will not be invalidating the election because of the duplicate voting glitch, but with Bloomberg’s latest poll currently showing Mr Macron and Ms Le Pen polling at 22.8 per cent, and far left Mr Melenchon at 18.3 per cent, it is possible an extra 500,000 votes either way could swing the balance of power.
Express.co.uk has contacted the French Embassy in London for comment and is awaiting response.