Major Adrian Agassi did not make the connection between the Bible, the land and the Jews when, fresh out of university, he left England for Israel in search of his roots. He was not even a practising Jew.

But over the past quarter of a century, the Israeli army lawyer and then military judge at the forefront of arguably the most significant battle in the occupied West Bank – the confiscation of Palestinian land for the construction of Jewish settlements – has come to see himself as in service of a higher duty.

In an unusually frank interview, which offers insights into the melding of religion, politics and law that underpins land seizures in the occupied territories, Agassi has laid out his belief that Israel has a biblical claim to territory beyond its borders and that he, even as an immigrant, has a right to live on it when those born there do not.

"When we [Israelis] say that this is a political conflict, then we lose the battle," he told the Guardian, adding that it should be remembered that the ancient land of Israel is "given to us by the Bible, not by some United Nations".

Agassi, one of the most important officials in the military courts wielding authority over large parts of the West Bank, says settling Jews on lands that made up ancient Israel stands above all other biblical commandments and only when it is done can they have "a promised land and a promised life".

"You say that these lands 'passed into Jewish hands'. Others would say that they came back into Jewish hands. Others would say that they are obviously ours, inherently," he said. It was, he claims, a mistake to call it the State of Israel. "If we would have named it the State of Jews, the Arabs would have understood that this land belongs to the Jews."

Agassi served in the legal department that oversaw the confiscation of land in the West Bank to build Jewish settlements and was then appointed to the military court that decided Palestinian appeals against the seizure of their property. The Palestinians almost never won. His court also ruled on legal disputes between Jewish settlers and Palestinians.

Agassi denies his credo affected his legal judgments but his court was considered so biased by some critics that on one occasion the military prosecution, in an unusual step, appealed against Agassi's ruling in favour of settlers to Israel's high court.

Agassi was born in Southgate, London, in 1964 to a family of rabbis from Baghdad. He studied law in the UK and emigrated to Israel at the age of 24 "with £500 and all of Bob Dylan's records". Four years later he found himself dragged into the first Palestinian uprising, the intifada, as a legal adviser to the military in the West Bank.

"I was very young and suddenly found myself in front of the stones and Molotov cocktail and the hate. I studied law, I had a liberal education, but I was at war and I knew we were right," he said. "I was 26 years old, I came from a foreign land. Those actions guarded our existence in the land of Israel. It lies at the heart of the conflict. It's a legitimate means to continue the works of our forefathers Abraham, Joseph and David."

Agassi says a peace agreement with the Palestinians "goes against nature" because as far as he can see nothing had changed in last 4,000 years in the land of Israel, and that back to biblical times Arabs and Jews were at each other's throats.

Agassi uses the term Arabs because he claims Palestinians do not exist.

He came to this conclusion over the past decade while serving as a special judge for administrative arrest. Based on confidential intelligence reports, without trial, Agassi sent several hundred Palestinians – deemed to be terrorists or security threats – to prison for six months or more.

"You read the raw intelligence material and you see that most of them are moved by religious doctrine, not by a political one. They use religion in order to justify killing as many Jews as possible. Is this not a religious war?"