The government said the three men were among six fugitives who had been hunted down and surrounded in the Shabwa mountains in eastern Yemen on Tuesday.
They finally surrendered to security forces yesterday in a dramatic development that coincided almost precisely with the opening of the trial.
The government alleged that the new detainees belong to the same group as the five Britons and one Algerian in court. Of the other people detained yesterday, two were Algerian and one Yemeni. The two other Britons were named by Yemeni authorities as Shaz Nabi and Ayyad Hussein.
The Yemeni government has been searching the country for Mohammed Mustapha Kamil, Mr Masri's 17-year-old son, ever since the British group was arrested in Aden last month. Yemen is demanding the extradition of Mr Masri from Britain on terrorism charges, seeing him as the mastermind behind a plot to bomb hotels, a church and the British consulate in Aden.
It also believes that Mr Masri was involved in the kidnap of 16 foreign tourists in Yemen last month, which led to the killing of three Britons and an Australian.
The trial opened with raucous courtroom scenes in which the accused shouted that they had been repeatedly tortured after their arrest in two downtown hotels in Aden on 24 December. "They have been treating us like animals," shouted Samad Ahmed, a 21-year-old student from Kingston University, rolling up the sleeves of his shirt to show dark bruises on both arms as he entered the dock. "Like animals," he repeated.
He and the other four Britons - Ghulam Hussein, 25, Mohsin Ghalain, 18, Shahid Butt, 33, and Malik Nasser Harhra, 26, - along with James Patrick Luovres, 30, an Algerian living in France, held an impromptu press conference with reporters in the moments before the judge entered the courtroom overlooking Aden's seashore.
Mr Ghalain, a student living in Shepherd's Bush, said: "For the first five days they wouldn't let us sleep. They battered us until we woke up." He said he was sexually abused. Mr Luovres, who sought political asylum from Algeria in France, said: "They made me sit on a bottle of Coca-Cola."
All the men looked apprehensive, but contemptuous of the proceedings as the prosecutor read out the charges in Arabic, which were haltingly rendered into English by an elderly translator. Of the Britons, only Mr Harhra, a student at London University, said he spoke some Arabic, but not very well. When the other defendants looked perplexed as the translator stumbled over a word, Mr Harhra grimaced and told them: "They just said we could be executed."
Before the trial was adjourned for three days so that the defence could consider the detailed charges, the prosecution said its case rested on the confessions of the accused, explosives found in their possession and three Yemeni witnesses. The accused all pleaded not guilty and said that their confessions had been extracted under torture.
Before the beginning of the trial an official entered the court carrying four hold-alls. From these he took five large, brown-coloured Russian- made plastic anti-tank mines, slabs of TNT with fuses, as well as computers and mobile phones which he placed neatly on a table in front of the judge.
The prosecution case is that Mr Harhra, who is of Yemeni origin, first entered Yemen last July to arrange for the others to follow him in December. They did so on 19 December and checked into the al-Wafa Hotel, in Aden before moving to a villa. They then travelled to Shabwa province east of Aden for military training. Later Mr Ghalain and Mr Harhra met Abu Hassan, the leader of the group which later kidnapped the tourists, and were given military equipment by him.
The prosecution also charged the men with belonging to Mr Masri's group, the Supporters of the Sharia, "which exports terrorism to other countries". The defence lawyer Badr Basunaid immediately protested, saying: "Abu Hamza is not on trial. He is nothing to do with this case."
After the charges were read all the defendants stood up to deny them. As the men were led out of the dock down a narrow stairs they shouted "bogus charges" and "kangaroo court". The judge said they should be examined by a doctor, moved to another prison and could see their families.
The Yemeni government is suspicious of the fact that one of the defendants, Mohsin Ghalain, is Mr Masri's stepson, and a second defendant, Mr Luovres is engaged to Mr Masri's sister-in-law Suzanne.
Together with Mr Masri's son who was arrested yesterday, three of the eight British prisoners now being held in Yemen have a family link to the controversial cleric.