Studying Computer Studies during the late 1960s and 70s might have meant never actually seeing a real computer. Machines made by the likes of IBM and ICL were big, (taking up a whole room), expensive and power hungry. The time devoted to processing secondary school student programs would be low, mostly when the computer wasn't in demand (e.g. in the evenings). Most programs would have been written on paper and then taken to the nearest computer centre partnering with the school. An operator would read the pieces of paper and produce your program as a set of punched cards or a roll of paper tape (depending on the input device that the computer you used had). These could be then input, with any output to a line printer. This printout could then be returned to the school, along with the cards or roll of paper tape so that pupils could see if their program had successfully executed.
If you were really lucky, you might have had a Teletype in your school that connected to the 'mainframe' via modem for interactive processing.
Computing in schools in the 1970s, exam papers and paper tape (BBC)
There is a large collection of ICL paperwork kept at the University of Manchester, including some ICL-CES items. Details here.
The BCS also have some ICL-CES material, mainly older material, but also some later newsletters that proves the newsletters ran until at least issue 41 (June 1982). As of writing on 15/12/2024, this site is no longer on line and I have changed the link to the archive.org copy. I have tried twice to get in touch with the Science Museum, with a view to viewing these newsletters. As of writing, they never reply.
CESIL.org - Ian Dunmore's site, with links at the bottom to his GitHub repo with his Python implementations of CESIL and CESIL "Plus".
Visual CESIL for Windows This runs on Windows 11 (Windows may prompt you to download the appropriate NET runtime, but it should do this automatically).
CESILPy - A CESIL interpreter written in Python.
CESIL interpreter for RTB. (Works on Linux, Raspberry Pi etc)