The information is not currently held.
The Home Office, Ministry of Justice and Attorney General's Office are currently working with the National Coordinator for Terrorist Investigations to improve the quality of data relating to those arrested, charged, convicted and imprisoned under terrorist legislation and under other legislation but considered terrorist related. As soon as this is complete a Statistical Bulletin covering this information will be published by the Home Office.
The bulletin will say how many individuals have been charged and convicted for encouragement of terrorism; however it will not break it down any further.