Was 'Westgate' Prison a real prison'

Saw this film in '47 when I was only six. A very powerful influence. My sister and I - through the rest of the '40's - would say back and forth to each other, "Yuh got that?!" It became a long-standing inside joke between us. Does anyone know where the movie was filmed? Someone said England. The prison itself looked real and yet not real. Exceptionally austere to a six year old. The high cold stone walls in evening rain, and other prison shots of impasse steel, looking almost a hideous cathedral, neither quite nouveau nor deco. So excessive in look, height and feel, it swooped over our little minds.
Was intrigued seeing it on DVD after so many years. Kept comparing the film's vantage from two consciousnesses: a child's unguarded openness vs. a degree of age-brought-on world-weariness.