During my time as an active JP I was not personally in a court from which a defendant had escaped although there were a couple of such episodes in an adjoining courtroom. In my very early days there usually was a uniformed police officer in the remand court and others in the vicinity as witnesses to one case or another. That level of security tailed off in the late nineties. Some docks were secure particularly in the remand courts but others presented no barrier to a determined miscreant who might have decided to abscond or do harm to those present. Recently two violent offenders breached what little there was of court security at Worcester Crown Court and Grimsby Crown Court respectively. I am a blogger and not a research statistician. There are no easily obtained statistics on the numbers of individuals who have attempted or actually achieved an escape from court. The nearest document of significance is listed below. It is not dated nor does it offer the aforementioned numbers; I would opine that that is deliberate obfuscation by the MOJ; a trait which has become the norm. When the numbers are hidden only the most dedicated will sniff them out. So just another result from the decimation of police numbers initiated by an incompetent home secretary who is honing her position as the most incompetent prime minister in my lifetime.
Not being sufficiently techie the link below should enable access of pdf. document.
The Management of Prisoners that present a risk of escape or violence ...
https://www.judiciary.uk/wp.../management_prisoners_risk_escape_violence.pdf
Annex 2 - Management of Prisoners who present a Risk of Escape or. Violence when attending Court - Application to Court for Improving Security. Arrangements .