Kind Hearts and Coronets : Question about the time line

I watched this movie the other day, and I noticed something. At the beginning, it has the notice with the date sometime in the 1800s. Later on in the movie, the Duke says something about the guy not being used to 20th century murder. I may have not heard correctly. Could someone clarify this for me?

I think it started in the very late nineteenth century, so that by the time Louis was an adult it was the early twentieth century.

the date you're referring to is the Capital Punishment Ammendment Act of
1868, the actual date of the execution is barely legible but it is definitely in the 1900's

The original novel, Israel Rank, was published in 1907; in the radio play (based on the film, not the novel) the date of Louis's intended execution is mentioned as being 1902.

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"An inglorious peace is better than a dishonourable war" ~ John Adams

In the film, General D'Ascoyne tells stories of his adventures in "The South African War". The only major war in Southern Africa was the Second Boer War (1899 - 1902), so it's reasonable to assume he had just returned. However there were quite a few campaigns and minor wars (such as the Zulu War) in the preceding decades, so it's conceivable he could have fought in one of them instead.

Whichever war the general fought in, the style of feminine dress, suffragette activism and the absence of motor cars on the roads point to the film being based in the early to mid Edwardian period (1901 - 1907).