Firstly just to say thank you to all who have contributed to this thread, the information was invaluable and allowed me to replace my coded lock without any major problems (took about 25 minutes).
Couple of notes whoever attempts this in the future;
Make sure you have your windows wound down and at least one door open before attempting this procedure if you don’t have a working remote. The reason being, as I found out, was that once the coded lock (aka lock barrel) is removed from the car, the plastic shaped “x” which it engages with was out of alignment, and took me a few minutes to work out what position it needed to be in (i.e. which way the “+” should be so it locked and unlocked correctly). Fortunately, with the windows down, I knew when the lock position was engaged as could see the windows rising.
Secondly, I’m not sure if it’s on the newer cars, but the allen key bolt that secures the coded lock is held captive by a plastic mount (fortunately for me as was worried this allen key bolt was going to drop into the door, and require me to strip it down). I also used the allen key bolt to gently help push the lock barrel away from the door, rather than lever it out from the outside of the door.
Good luck to all who attempt this procedure, the instructions on this forum saved me a lot of time and money.