Harry Shindler, who lives in Italy, as well as 12 other Britons from different member states, will argue that the referendum was discriminatory and illegal as they were denied the opportunity to vote, along with a million other expats.

Mr Shindler’s lawyers will allege they were treated like “second-class citizens” and were deprived of their right to vote on the basis they exercised freedom of movement.

“I’ve been asked to go to Luxembourg but I’m 97 and I restrict my travelling,” Mr Shindler told The Guardian from his home in Porto d’Ascoli.

“I’ve told them I will be by my telephone if they require me to testify.”

Mr Shindler served in Italy during the war, taking part in the liberation of Rome in 1944.

He married an Italian woman and returned to the country upon his retirement in 1982.

He was awarded an MBE in 2014 for services to Anglo-Italian relations.

Julien Fouchet of Cornille-Pouyanne Avocats, is representing Mr Shindler. He will tell the court the EU’s negotiations should not take place as the British negotiators are not representative of the British people.

“By adopting the contested decision has allowed a withdrawal procedure to be initiated without expatriate European citizens having had the opportunity to set out their views on the possible loss of their European citizenship,” Mr Fouchet’s submission to the ECJ states.

“The right to be heard and to express one’s opinion by way of a vote in the event of an election with a European scope has thus not been respected.”

The European Council has said the applicants have no standing.

Mr Shindler added: “If we win this, that’s the end of Brexit because Mrs May will arrive with her negotiators and there will be no one for her to negotiate with.”