In the collective unconscious of western civilisation, the name Judas Iscariot epitomises the word "traitor" like no other.

Judas supposedly condemned Jesus to a gruesome violent death sentence by crucifixion: selling him out for a paltry 30 pieces of silver. Then, wracked with guilt, Judas hung himself from a fig tree.

For Jews, Judas is the elephant in the room. He's almost taboo in Jewish literature, history or academic study, probably because he is the archetype for antisemites: the turncoat Jew who values money over loyalty.

In Amos Oz's latest novel, Judas, the central protagonist of the narrative, Shmuel Ash - a diffident young radical intellectual - has an obsession with Judas Iscariot.

Shmuel believes that Judas was the most loyal of Jesus's 12 disciples and that his betrayal of Jesus was fabricated by the later gospels for political reasons.

So why, at this late stage in his career - after publishing 19 novels, six books of non-fiction and one children's book - did Oz decide to explore the subject of Judas, and his rather complex relationship to both Christian and Jewish culture?

"Well, the way you phrase the question, it sounds like I wrote an essay exploring the subject," Oz replies, lounging back on the sofa, coffee cup in hand.

"Fundamentally, this is a story about three people, changing each other a little bit. However, one of the ideas that obsesses the protagonist is the question of loyalty and betrayal.

"Judas is the archetype of a traitor," Oz explains. "You call someone Judas: you spit in his face. Not in my language though. In Hebrew, it's very common. My father was Judas. My son's name is Judas too."

In Israel, the book is called The Gospel according to Judas, with Judas spelled in Hebrew "Yehudah".

"The famous 30 pieces of silver, the kiss, the god-killing, the whole story is unlikely, even from a purely detective point of view," Oz argues, "so my protagonist offers an alternative story."

Intriguingly, Oz maintains that, throughout history, traitors are usually those who have been way ahead of their time.

Judas is set in Jerusalem during the winter of 1959-1960. The story explores the rather strange relationship between three odd individuals: Shmuel Ash, a young student; Atalia Abravanel, a flirtatious femme-fatale type, twice Shmuel's age, who eventually seduces him and treats him with contempt, pity, love, and curiosity in equal measure; and Gershom Wald, an elderly invalid, who has a passionate zeal for Israeli politics and history.

While Oz is fairly reluctant to talk about actual Israeli politics, the subject is almost inescapable. He has been a consistent advocate for a two-state solution, and helped set up Peace Now in 1978 - though, these days, Oz doesn't consider himself a pacifist. In recent years, Oz has become a vocal campaigner for the left-wing, social democratic Zionist party Meretz.

Is writing in itself a political act, I ask. And are history and politics almost an obsession with Jewish writers, particularly Israeli writers?

"For my people, history is not something that happens across the television screens. Violence; war; persecution; antisemitism; blood libels - those things changed the lives of my family, my ancestors and myself."

Oz, at 77, has an intensity, frankness, and brashness to his demeanour that is strangely intimidating, though appealing and charismatic, too.

There is a moment in the novel where Shmuel and Gershom begin talking about Israel's founding father and first Prime Minister, David Ben Gurion. Wald says: "I consider Ben Gurion the greatest Jewish leader of all time."

Does Oz concur?

"We should be very careful of identifying me here with this or that character," the author insists, almost as though I am trying to draw him into a trap.

"There is an assembly of voices in this novel, and they collide and contradict each other.

"I merely wrote a piece of chamber music. It's wrong to ask the composer after the concert: excuse me, are you behind the violin or the cello?

"I don't completely agree with everything my characters say but there is a certain component of myself in each of their conflicting ideas."

Oz points his finger at me, as though I have overstepped the mark and continues: " So, please, don't try to look for my bottom line in any one of my characters."

He adds: "I can tell you my opinion about Ben Gurion. But we have to draw a very thick line between the discussion of my novel and the discussion about him specifically.

"I think Ben Gurion was one of the greatest statesmen of all time, and not just in Jewish history.

"He was a sensitive man, who sensed that the Jewish people had the worst political cause in the world: no country, no power, and no family of nations either.

"Jews never had genuine gutsy supporters. They were hated and despised throughout history by most. To navigate a vehicle, which initially had hardly any wheels, and seize a unique momentary opportunity to create a Jewish state: this is greatness."

Ben Gurion's strongest attribute, Oz insists, was his unique sense of timing, and the ability to distinguish between the possible and the impossible in the art of politics.

But surely he made many mistakes, too? What about Ben Gurion's decision to form a special bond during the Cold War with the United States. Ultimately - many of Ben Gurion's greatest critics have pointed out - this led to the creation of an Israeli state that became obsessed with military force.

Others claimed Ben Gurion had little sympathy for Palestinians, with little interest in making peace.

" Like any statesman who [accomplished great] things," Ben Gurion made mistakes." Oz admits. "Are there regrets in his record? Yes, there are. But he is one in a million. I think Israel owes its very existence to the vision and determination of this little man."

Back to Judas, the topic of conflict between Arabs and Jews comes up frequently in the many conversations between Shmuel and Gershom and, in one of these, Gershom mentions a radical intellectual friend of his who was often called a traitor for insisting that there surely must have been a deep historic basis for ties of sympathy and understanding between what were essentially two victims of Christian Europe. Is this an idea that Oz agrees with?

There is a long pause before he answers.

"In an ideal world," he says, "victims unite and march together. And yes, Jews and Arabs, in different ways, have both been victims of Europe.

"Europe suppressed the Arabs through imperialism, colonialism, exploitation and humiliation.

"And the Jews were halted throughout Europe for thousands of years, through antisemitism, the Inquisition, pogroms, and then an unprecedented genocide."

"I wish this would have turned the Jews and Arabs into brothers and developed a sense of solidarity. But, as often happens with former victims of the same oppressor, they look at each other and they see the bad guy."

In the novel, Shmuel also makes the suggestion that, for thousands of years, while Jews certainly knew the power of books, prayer, trade, scholarship and tradition, they never really experienced real power. At least until the state of Israel was formed in 1948.

And then when they got power, Shmuel insists, they got drunk on it. The more I press Oz on the opinions of his characters in Judas, the less reticent he actually seems to become.

"Look," he says, "a guy that suddenly gets hold of a big heavy hammer, he tends to think that every problem in the world is a nail. Not every problem in the world is a nail. It's good to have a hammer. Sometimes you need it. Some problems are nails. But many problems cannot be resolved by military force alone.

"And[typically] the Israeli Jews tend to be intoxicated with military force because, quite frankly, they never had it. Because the only real power they saw [was] on their poor beaten backs for hundreds of years.

"Now they have power, they get carried away. It's only natural. It's what you would expect. But I think it is very crucial for the Israelis to realise that certain things cannot be done by force: not with a hammer and not with a machine gun."

The main problem Israel faces, Oz suggests, is how to be accepted in the neighbourhood of nation-states in the Middle East.

"I am not a pacifist," he insists. "I am not against having a big hammer in your hand. As long as you remember that this big hammer is not the solution for everything."

We're reaching the end of our discussion now and I recall that Oz started out the interview by claiming this latest novel was an act of optimism.

"In the beginning of the novel," Oz reminds me, "the three characters are on different planets.

"In the end, they all change a little bit.

"This is not universal redemption. It's just three people. This is not salvation either. But it is a change. This change is a testimony to my own basic optimism about human nature."

So does that optimism extend beyond his fictional characters? To art? To mythologies? To words on paper? What about the real events the characters discuss non-stop throughout the book: politics, history, war?

These are never-ending topics of debate in an ever more chaotic and unpredictable Middle East, including Israel

Again, Oz approaches the answer with caution and restraint, but then doesn't hold back.

"There are hundreds of millions of enemies- mostly in the Muslim world - who would like Israel to disappear. No other state faces such hostility," he says. "Not even North Korea or Iran.

"Even in the worst days of Nazi Germany, nobody in their right senses talked about eradicating Germany. But there are many people in this country, and in this city, who talk about the serious need to eradicate Israel. This is scary."

"I don't believe in miracles," says Oz. "I don't believe in salvations. But yes, I believe that people can change. Sometimes even for the better. So I am an optimist. But not on the monumental scale."