Why does Judas get such a bad rep?

In Christian tradition, Judas was the follower of Jesus who betrayed him to the Jewish authorities. The four gospels leave his motives uncertain but his name has passed into common usage as a synonym for personal betrayal. "Judas" was what some folkie shouted at Bob Dylan when he set aside his acoustic guitar and went electric.

Isn't he the classic baddie?

Every story needs a villain and Judas offers an archetype with his traitor's kiss.

The trouble is that the modern fashion is not for heroes but for anti-heroes. And Judas makes a handy one of those too, hence the new book by a very odd couple, the perjurer-novelist Jeffrey Archer and one of the world's top biblical scholars, Professor Francis Moloney. A very unholy alliance. They have just written The Gospel According To Judas, which portrays Judas as traduced by the gospel writers since he was really trying to save Jesus from "an unnecessary death".

So he may have been a goodie. Does that add up?

As much as any of the scores of weird and wonderful theories that people have come up with over the years. The gospels say so little about Judas that it's possible to project pretty much anything on to him.

Why was Judas such a figure of mystery?

Three reasons. No one is sure who he was, exactly what he did or why.

First, he was maybe the only apostle with a surname . . . Iscariot. But does it mean "man from Kerioth", implying that he was a Judean, unlike all the other key followers of Jesus, who were Galileans? Or does it suggest Sicariot, from the Latin sica, meaning dagger, suggesting he was one of a group of fanatical nationalist zealots who thought that the only good Roman was a dead Roman. Or is it just a Hebrew-Aramaic inscription meaning "the one who is to hand him over".

Second, no one is sure what his job was. Two gospels suggest he was the man who carried the money for Jesus. All four evangelists insist he was a full apostle . . . he is repeatedly called "one of the 12" and is often reported as present at key moments . . . which suggests that Christ saw in him "some good qualities and the gift of no mean graces".

Third, most mysteriously, what was his treachery? The gospels say that he lead the authorities to Jesus. But it is not much of a betrayal since Jesus was not exactly in hiding. He had been publicly teaching in Jerusalem all day. It would hardly be worth the legendary 30 pieces of silver . . . enough to buy a field.

All these enigmas have led to countless attempts over the past 2,000 years to lay some intelligible explanation upon the origin and motives of Judas.

And now the most reviled man in history has a new champion in one of the most reviled men of recent years: Jeffrey Archer.

Wasn't the real Gospel of Judas found recently?

A 62-page codex, carbon dated to about 300 AD, but believed to be copied from an earlier document, was unveiled last year.

It was in the same Sahidic dialect of Coptic used in the Dead Sea Scrolls discovered in 1945 (which included the Gospel of Thomas). The church does not accept the Dead Sea Scrolls as divinely revealed but they still prompted a major re-evaluation of early Christian history.

What did it say?

It said that Judas, far from being Jesus's enemy, was his chief apostle, who was acting at Jesus's request when he "betrayed" him to the authorities. Without Judas's help, Jesus would not have been crucified and God's plan to save mankind from its sins could not have been fulfilled. Someone had to do it, to fulfil Old Testament prophecies, the early Christians believed.

Judas was the chosen one.

That was why the early Gnostic sect known as the Cainites venerated Judas.

To them he was a kind of saint. It's a notion which has repeatedly resurfaced through history, most recently, perhaps, in the film The Last Temptation Of Christ.

But this is far from the only solution offered to the mystery.

What other excuses have been made?

Many have speculated that Judas assumed Jesus was the messiah come to liberate the Israelites from Roman occupation. Then, when Jesus kept saying, "My kingdom is not of this world, " Judas betrayed him out of disappointment. Others have suggested that Judas may have thought the arrival of armed guards to arrest Jesus would push him into launching his anti-Roman rebellion or provoke a rising of the people to set him free. Theologians and artists have had fun with all this for centuries.

Can a novel help?

Moloney thinks it can. This former president of the Catholic Biblical Association of America and member of Pope John Paul II's International Theological Commission for 18 years candidly admits that scholarly works such as his own "had made little impact on the increasing scepticism surrounding the Christian church" prompted by "deeply flawed and uninformed works including Dan Brown's The Da Vinci Code and Richard Dawkins' The God Delusion".

So can Judas be rehabilitated?

That depends on whether, in the end, you think his motives were malign or just misguided. But the gospel according to Jeffrey will not help much because it plays into a distinctly modern error. It is that of reading the gospels as if they were novels, from which we expect telling biographical detail and revealing psychological motivations. The New Testament was written in a different era. It is to be read as poetry, philosophy and theology.