[ghaff]

To some degree, I'm sure it was a plot device but 19th century English novels often depended on rapid/same-day communications via letter at least in the environs of London.

[hdjdbtbgwjsn]

That was considered standard then in London. Royal Mail even had its own underground railways in London.

[eru]

Compare https://en.wikipedia.org/wiki/London_Penny_Post