Domenico Rancadore, 64, is wanted in Italy to serve a seven-year jail term for his role in the Sicilian mafia. Known in the mafia as "The Professor", he had been on Rome's list of most dangerous criminals.
Rancadore had been living in a modest suburban house in west London under the name of Marc Skinner, with his English wife and children, when he was arrested on August 8th.
He was denied bail for a second time at Westminster Magistrates' Court in London on Thursday after prosecutor Aaron Watkins argued there were "overwhelming grounds" to suspect that he would go on the run again if granted bail.
The court heard that Rancadore had told British officers upon his arrest: "I'm not going back, they will kill me."
Watkins said it was "telling" that Rancadore, a former teacher, had spoken openly of his unwillingness to return.
Wearing a rugby shirt, Rancadore clutched a white Bible as he listened from the dock.
He shook his head as the judge denied his request for bail, and exchanged glances with his wife Anne Skinner, who was watching from the gallery.
Rancadore had offered his wife's home as a surety for bail, along with £10,000 (€11,700), the court heard.
Judge Quentin Purdy told Rancadore: "It seems to me clear that if you are released on bail there is a risk you will disappear.
"I can see no grounds to grant you bail and be satisfied that you will return."
Rancadore will appear before the same court on September 20th, Purdy said.
Prosecutors told the court earlier this month that Rancadore was a leader in a gang that "spread terror" on the Italian island of Sicily, "systematically murdering anybody who did not comply with the will of the members of the organisation".
But defence barrister Alun Jones questioned on Thursday whether he had a senior role in the mafia.
Rancadore suffers from high blood pressure, angina and reflux, Jones added.
"In our submission a man in this condition, with family ties to this country, with his wife's house and £10,000, is not going to abscond," he told the court.
Rancadore was convicted in his absence of Mafia links in Italy after he went on the run and moved to Britain in 1993.