The police will know what goes on in shops both Thai & Chinese.
In the main they will turn a blind eye as it provides a service which, to put it bluntly, reduces "frustration" in the male population. If they close that method of "release" then they know they could create themselves more problems elsewhere.
However, if someone makes a complaint then they are obliged to investigate.
If the shop is clean, the ladies are all entitled to work there, e.g. have Visas etc, then they'll leave them alone.
Who complains?
A "snooty" resident who doesn't want "shops like that" in Dorchester?
A "wannabe politician" who wants to make a name for themselves?
Someone who has read about raids elsewhere, e.g. Swindon a couple of weeks ago, and assumes all shops are the same?
A disgruntled customer who makes a "revenge" report?
All massage shop owners know that their very existence is always on the line.
If they stay strictly legit then they are unlikely to get enough custom to remain viable, if they offer extras then there is always a risk of being closed.
It's why I get annoyed with those who post, "Oral?", "FS?".
If you want those services then go elsewhere. It's those posts, customers that cause shops problems.