I saw a Mk301 at ironbridge museum, when I was about 10 years old.
Stood above me on a plinth, I could just reach the door release lever (that bit bolted to the door) but, as it wasnt plugged in, nothing happened.
It was a slightly sprung metal lever that you nudged against the edge of that metal plate. Weird set up.
Went back to search for it last summer and couldnt find a trace of it. All I assume is that it was probably Servis' own museum example, that they loaned out for an exhibition. God only knows where that machine is now:-(
Paul