Personally, I headcanon them to be Southeast Asian, maybe Burmese. Burma, currently known as Myanmar, was a British colony and there were a few different Anglo-Burmese fought in the Victorian Era (which I will continue to believe N was born in until told otherwise).
M would instantly struggle and demand to be put down…and then threaten the Detective that if they ever tell anyone about it then it won’t end prettily for them…M is so charming, lol.
This sounds like my brother’s cat. (Now that I think about it, Skitts also hates everyone (except my brother, to whom he show occasional affects) and hides in dark corners.)