As there are a lot of misconceptions about the Clerk of Works selection I will explain what happens for the Clk Wks (C) selection from being to end (there might have been some slight changes but this is the general gist):
Class One tradesman
Class One Combat Engineer (can be Class Two if a POM)
Min rank LCpl with recommendation for promotion to Cpl
Field Section Commanders Course (a nice to have, I'm not sure if this is a requirement for POM, especially if you have passed your Plant Section Commanders)
SNCO CLM (AEC part)
SC security clearance
Have 8 years residual service left upon successful completion of the course.
There is no requirement to have come top of every trade course you've been on or have been recommended since your Class Two. If you are interested; apply.
About 10 months before the course is due to start a notice goes on unit orders inviting all personnel who are interested in Clk Wks training to register their interest and pick up an application form. On the application form you will put details about trade courses, trade experience, operational experience, leadership and command appointments you have held. You will have an interview with your OC and Clk Wks (C) in your CSC. You will also have a CR raised. You need to be approved by your OC, Clk Wks (C) and be recommended in the CR that has been raised. Assuming that is the case you will then get called forward to Chatham for a 2 day assessment.
The morning of the first day is taken up with exams. English tests including basic SPAG and the ability to express yourself on paper. Maths is up to A-Level standard including questions on quadratic equations, 3d triganomtry and transposition of formula. There are a couple of techincal drawings that you need to look at and work out what they are. There are also logic questions such as if the cog turns this way what way will the other cog turn.
Once you've done the exams you will then be interviewed by the SMI (C), AI and CI PEW. They will ask questions about your experiences within the Army, why you want to be a Clerk of Works, course content and career pattern following successful completion of the course.
The next day there is a BFT. I'm not sure what the current policy is on downgraded personnel applying. I believe there was a push to stop downgraded personnel applying because of current operational commitments. You will also finish off the interviews.
A few weeks after the selection a board will sit in Glasgow to decide who is loaded onto the course. There are three options; loaded onto the course which is starting in 10 months time, defered with a recommedation of which course number they should apply for (normally for those lacking trade and/or command experience) or not selected & don't reapply.
For those selected if they will be automatically loaded onto any courses that they require such as JCC and SNCO CLM. There is also a pre-course work book to help get you up to scratch on maths and English.
Whilst the course is certainly hard it is not impossible, you don't have to sacrifice every waking moment to work and you don't have to become a hermit. You also get to remind the general roster how good high band Staffy wages are!
Hopefully this has answered your question there Solstice. Realistically you are looking at having been in the Army for at least 8 years (if you have plenty of experience on tour, trade experience etc) and maybe a bit longer if you don't.