There are a few clues that have been picked up once Thomas had identified Lai Chi Kok as the area with the most potential so I'll go through a few of them. First off is the hilly terrain and the shaved slopes in the background. The shaved slopes are actually the area cut out to accommodate Cheung Hang Road which winds its way up the slope. The road the trucks are coming down is Butterfly Valley Road but it is hard to recognise it now due to all the roads that have been constructed here. The major one is perhaps the Tsing Sha Highway who's flyover now covers this whole area even up into the valley beyond.
The village that can be seen on the far side of the road in the second picture is Wai Man Village. It sat on the other side of a waterway which is why you can see a crowd piled up against a railing in that same picture - they couldn't get any closer without falling into the unseen water. Sadly, the village was removed soon after this film was made to make way for the construction of the Ching Cheung Highway (circa 1967) that now snakes around the side of that slope.
The white industrial building in the background of the lowest picture used to sit on the corner of Kom Tsun Street and the very end of Cheung Sha Wan Road but has since been replaced by another one called Grandion Plaza. The only anomaly I can find in all this is a missing building that should be this side of it called the Tong Yuen factory Building. According to building records (Centamap) it was built in 1963 but is obviously missing in the picture above so I can only surmise that perhaps that date reflects when construction commenced rather than when it was finished. Either that or the supposed filming dates for the film are wrong (see bottom of page here). I am inclined to think the build date was wrong simply because I am not sure that industrial/factory buildings are issued with an occupational permit which normally forms the basis for the build date on residential buildings. I am willing to be proven wrong though so feel free to comment if you know what the deal is.
Anyway, you can look at the following Streetview to see how the area has changed. The picture below shows us looking up towards the hills in Butterfly Valley similar to the second and third pictures above. The prison was redeveloped into its current "correctional Institute" sometime in the late 70's/early 80's.
With regards to the interior of the prison, I am still awaiting confirmation but believe Arthur may have identified it correctly as the current Museum of Coastal Defense in Shau Kei Wan. I just need to make a trip there to size up the angles. Stay tuned.