The court hearings were held in secret and under the tight restrictions of Turkey’s counter-terrorism laws.
But the allegations of Islamic State terrorism being heard near Istanbul are the most serious ever to be made against a British citizen in court.
A former Tube driver is the main suspect in this alleged plot.
Aine Davis, a 32-year old from west London, is accused of becoming a senior IS commander.
Court files unearthed and translated by ITV News say he is "considered to be in charge of Daesh (IS)".
Never before has an alleged IS figure of such notoriety been brought into custody.
Guilty or not, faced with the growth of terrorism on its doorstep, Turkish authorities are likely to judge his arrest as an important development.
Davis came to attention in 2014 when his wife, Amal El-Wahabi, became the first person in Britain to be convicted of funding jihadis in Syria.
She was jailed for hoodwinking an old school-friend into agreeing to take 20,000 Euros to Turkey for her husband.
But it was subsequent allegations that made him notorious among British counter-terrorism officials.
As an alleged member of a gang of IS prison guards that included Mohammed Emwazi – known as ‘Jihadi John’ – he became prominent.
The road to Raqqa is well-trodden. Several hundred British citizens are thought to have travelled to the so-called caliphate.
But bringing jihadists to justice for crimes committed in the juridical vacuum of Syria is almost impossible.
In the age of Islamic State, allegations of this magnitude are barely heard in court.