Marine Le Pen's general election hopes could be in peril after it was revealed 500,000 voters outside of France were sent duplicate polling cards - giving a traditionally non-right wing electorate the chance to vote twice.

Because Le Pen's Front National party appeals to a conservative, domestic community the computer error could potentially see the politicians first round vote overshadowed by pro-EU double-voters.

French authorities confirmed they would not be investigating the potential electoral fraud until after the election, when retrospective prosecution may take place.

Marine Le Pen's general election hopes could be in doubt after a computer error meant 500,000 duplicate polling cards were sent to overseas voters - many of whom oppose the Front National

French authorities confirmed they would not be investigating the potential electoral fraud until after the election, when retrospective prosecution may take place

By which time Le Pen's hopes for a Front National victory could already be extinguished.

London has such a vast French community it would constitute France's sixth largest city.

Some 300,000 French people live in London, many of whom appear to support centrist politician Emmanuel Macron.

An Ipsos-Sopra Sterna poll indicate Macron and Le Pen are tied for the lead on 22 percent each meaning a swing of 500,000 votes against the Front National leader could swing the election entirely.

Far-left candidate Jean-Luc Melenchon and conservative Francois Fillon on 20 and 19 percent respectively.

Jean-Luc Melenchon, who has surged in the polls could also benefit from this catastrophic error.

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.'

Fears among Le Pen supporters have grown because the glitch could give a traditionally non-right wing electorate the chance to vote twice. Some 300,000 French people live in London, many of whom appear to support centrist politician Emmanuel Macron

The punishment for voter fraud can be up to two years in prison and a fine of about £13,500.

However police would only only be able to find out if they run checks on individuals through the computer systems.

Despite the glitch, it remains unlikely that the polling cards would be used in significant enough numbers to alter the outcome adversely.

France’s Interior Ministry has confirmed he will not be invalidating the election.

The two highest scorers in the first round on April 23 will go through to contest a run-off on May 7. The race has been tightening for weeks, even though centrist Emmanuel Macron remains favourite.