Online chess players have a notoriously hard time against Israeli opponents. And here, for the first time, we can reveal one of the reasons why.

Natan Sharansky, the former Soviet dissident who has beaten former world chess champion and Grandmaster Garry Kasparov, takes on random opponents online, working under an assumed username.

I ask him to reveal his username and he responds with the same trademark smile he used when telling his jailers to leave him alone because he was playing chess in his head. “No, then it will not be anonymous,” he says.

For Sharansky, the most famous of the refuseniks who fought to leave Soviet Russia for Israel, playing chess here is one of his biggest pleasures. The game kept him sane through his imprisonment, and he now takes great joy in playing it in “the Jewish paradise”.

“It was my very important method of survival,” he says, explaining how he would play mentally, without a board or pieces. “I spent a lot of time in solitary confinement, more than anyone else I know: 405 days. And in the small, dark punishment cell where it’s very cold and you’re very hungry and there’s nothing to do, you are supposed to go mad.

“It is supposed to disintegrate your intellect, but instead of this I played thousands of games of chess, won all of them, and improved on the previous player’s game. So instead of degenerating I was becoming stronger intellectually.”

He actually used his chess-mind in his 125 interrogations, when he considered what his aims were in every word he said before responding.

This Independence Day is a high-point for Sharansky, as he will receive the country’s highest civilian honour, the Israel Prize, for lifetime achievement. In normal years, too, springtime is a poignant season for his whole family. The freedom theme of Passover means a lot in the home of a former prisoner, and they hold a “seder” on the date of the anniversary of his release, when his family gathers, enjoys a thanksgiving meal, and tells the story of his suffering and the campaign for his freedom.

And in Sharanksy’s story, chess is ever-present. He says: “Chess has been my biggest hobby since the age of five because it gave me a field in which I could think and make decisions freely without fear of punishment, and it gave me power over the people who are taller than me.”

He adds that he had “a theory that the taller the person, the quicker I would win”.

Sharansky is about to wind down a 45-year stint leading various Jewish causes this summer, when he retires as head of the Jewish Agency. And what strikes me as we finish our conversation is how his chess strategy reflects his approach to his Jewish causes, from fighting for freedom from the Soviets to promoting Israeli-Diaspora ties.

What is his advice to young upcoming players? “Keep as many options open as possible, keep the initiative, be ready to change the plans but never change your strategic aims.”