British Prime Minister Boris Johnson’s father is in the process of applying for a French passport to maintain his European ties.

Speaking on French radio RTL, Stanley Johnson, who voted Remain in Britain’s 2016 referendum, said he wanted to become a citizen of France because he already has family links to the country.

“If I understand it correctly, I am French," he said.

"My mother was born in France, her mother was totally French as was her grandfather. So for me it is about reclaiming what I already have. And that makes me very happy..."

The 80-year-old, who spoke in French during the interview, said he would always be a European. 

"One cannot tell the British people: you are not Europeans. Having a tie with the European Union is important,” he added.

His passionate Brexiteer son spearheaded the Leave campaign in the 2016 referendum.

Brexit becomes a reality on Thursday as Britain leaves Europe's customs union and single market, ending nearly half a century of often turbulent ties with its closest neighbours.