Even native British ears from outside London struggle. Subtitles decode this. They transform mumbled slang into sharp, witty text. Seeing the words flash on screen makes the insult land with twice the comedic force than merely hearing a murky growl.
Today, if you stream the film on high-quality platforms like the Criterion Channel or the restored Paramount Blu-ray, the subtitles are generally "better." They respect the slang, they don't censor the dialogue, and they capture the wit of the script. the italian job 1969 subtitles better