Frankly, hearing Lockwood’s impression of what Cracknell was doing on set, it’s actually kind of miraculous that the movie was actually finished.
The entire room erupted in laughter when Gary Lockwood did his impression of Derek Cracknell, mostly because the contrast is just so extreme.
HAL 9000’s voice is widely recognized for its quietude and serenity — which winds up perfectly balancing against his seriously sinister acts — but you get absolutely none of that with the cockney accent.
With this knowledge, the performances by both Lockwood and Keir Dullea are frankly even more impressive in retrospect, as it’s kind of amazing that they didn’t just burst out laughing every single time they shared a scene with the movie’s killer artificial intelligence.