Muslim convert Richard Dart is facing a long prison sentence admitting getting involved in terrorism.
Dart became involved in extremism after converting to Islam. He was featured in a BBC Three documentary made by his stepbrother.
He pleaded guilty at the Old Bailey with Imran Mahmood and Jahangir Alom to engaging in conduct in preparation of terrorism. They plotted to go to Pakistan to train at a terrorist camp and to travel abroad to commit acts of terrorism.
The three bearded men appeared by videolink and were remanded in custody by Mr Justice Simon for reports before being sentenced, on a date to be fixed.
Dart, 29, of Broadway, Ealing, west London; Mahmood, 21, from Dabbs Hill Lane, Northolt, west London; and Alom, 26, of Abbey Road, Stratford, east London, admitted being involved in the offence between July 2010 and July last year.
The case against them was that they intended to use their training to attack targets. Mahmood, who had been to Pakistan before, was able to offer advice and assistance. Police recovered bits of text messages from a computer in Dart's home which referred to "even to just deal with a few MI5 MI6 heads".
Dart, the son of teachers from Dorset, appeared in the film My Brother The Islamist by Robb Leech. In it, Dart is said to have been turned into an extremist in months after joining the Muslims Against Crusades group and listening to controversial activist Anjem Choudary. He changed his name to Salahuddin al-Britani. He worked as a BBC security guard.
Alom, who lives near the Olympics site in Stratford, was arrested in July along with his new bride Ruksana Begum, a woman whose family has extensive links to terrorism. In December she was jailed for a year at the Old Bailey for having al Qaida terrorist material in her mobile phone. The link between them could not be made until Friday when a court order was lifted.
Begum, 22, who has a first-class accountancy degree, had been married for a month when anti-terrorism officers raided their home. The court heard that Begum's brothers, Gurukanth Desai and Abdul Miah, pleaded guilty to a plot to blow up the Stock Exchange and were sentenced in February to a respective 12 and 16 years in jail.
Mohammed Chowdhury, jailed for 13 years for the same December 2010 plot, asked to marry her but she had never met him. She married Alom in June last year and moved from Wales to London with her new husband.