OMG!
I used to have this game on my Spectrum when I was about 10 or 11 - what an amazing game this was!
I remember it lost "Crash's" game of the year award to Starfighter
This clearly should've won! In my humble opinion of course! Ha ha!!
Anyway, I haven't downloaded this version yet, but I do remember a "hidden" key that helps a lot...
Go to the South-East of the main prison yard, along from where you enter the exercise yard, and you come to a guard post.
Under one of the legs of this guard post is a key... look hard, it's there!
Grab this one, I remember it opens a few doors that are only otherwise openable with the wirecutters and saves a lot of time/frustration!
Off to download it now...