You have test equipment so use it and check the earth loop impedance if under 0.35 likely it's TN-C-S if under 0.8 then likely TN-S and above 0.8 likely TT what reading do you get?
You are talking about the
Ze here. But, when looking solely at the Zs, it is often impossible to say. I would say the first two are a reasonable test for their respective supply types (if they are wildly out, there is a problem the DNO needs to be called out to investigate). However, TT installs
can (but not always) present decent sub-1 Zs readings due to parallel paths with various types of bonding. Just something for the wary to watch out for!