I am a home office police officer
I once raided an establishment like one of those mentioned above (to be clear:- not one mentioned above, but with low standards) looking for illegal workers
We found them sleeping in the basement kitchen around the cauldron where they cooked their grizzle
Yes ... one big cauldron full of oil and spices and heaven knows what. With little sieves full of the meat. So cheicken, lamb, and even fish cooked together.
We also saw some mice hanging in the cauldron
We took the illegals to the detention centre. That establishment was not open for a couple of days then opens again with new staff in there
Apparently, putting mice in the cauldron is considered good luck in some countries
As I say, not the above-mentioned places but my point is in London, some standards can be very low.